The medical scholars during the medieval Islamic era placed great emphasis on the value of dissection and the knowledge of anatomy for the diagnosis of affected organs, the relationships of the organs to one another and the application of adequate medical and surgical treatment...
Editors Note: This article is a chapter extracted from a book whose draft was completed by Professor Rabie Abdel-Halim just before passing away on Wednesday 15th April 2015, “1001 Cures: Introduction to the History of Islamic Medicine” as the second in the series of 1001 Cures books with this article “Remedies” from Chapter One, Pages 26-32, published by the Foundation for Science Technology and Civilisation (FSTC).
The medical scholars during the medieval Islamic era placed great emphasis on the value of dissection and the knowledge of anatomy for the diagnosis of affected organs, the relationships of the
organs to one another and the application of adequate medical and surgical treatment. Thus, they emphasised that the doctor should be quite knowledgeable in anatomy. Hence, Abū ʿAlī al-Ḥusayn ibn ʿAbd-Allāh Ibn Sīnā (Avicenna, 980–1037) made it clear that, if the medical treatment for a bladder stone fails and the cutting operation had to be carried out, one must choose the one who “knows the dissection of the bladder, the places where it is joined at its neck by the semen channels, and the related vessels so that he could prevent what he should keep away from, such as causing an inability to reproduce or heavy loss of blood or a fistula that does not heal”.1 Also Abū al-Qāsim Khalaf ibn al-ʿAbbās al-Zahrāwī (Albucasis, 936–1013) in the thirtieth maqalah of his encyclopaedic work al- Tasrīf, devoted to surgery and surgical instruments stated that: “He who is not skilled in as much anatomy as we have mentioned is bound to fall into an error that kills a human being.”2,3,4 Similarly, Abū Marwān ʿAbd al-Malik ibn Abī al-ʿAlāʼ ibn Zuhr (Avenzoar, 1093– 1162) emphasised the great importance of practical knowledge of dissection in the following warning in his book al-Taysīr, in the course of discussing the management of inflammatory swellings of the neck when ripe and ready for bursting or drainage: “And in case you have mastered the science of dissection, then drain by the scalpel in the way that you will not come across a vein, artery, nerve or anything whose injury will lead to an extra harm to the patient”.5 In addition, Alāʾ al-Dīn Abū al-Ḥasan Alī ibn Abī al-Ḥazm al- Qarshī ibn al-Nafīs (1210–1288) allocated a special chapter in his book, Sharḥ Tashrīḥ al-Qānūn, entitled On the Benefits of Studying the Science of Anatomy, and showed how essential this study is for reaching diagnoses and for practicing medicine and performing different surgical, orthopaedic or ophthalmological procedures.6 Furthermore, in this book he wrote a special chapter on the best mode for dissecting the following parts: bones, peripheral vessels and internal organs of the chest (heart, lung, big vessels and the diaphragm).7
In fact, all the eminent Islamic physicians and the theologians of this era stated that knowledge of anatomy leads to a deeper appreciation of God’s wisdom and omniscience.8,9,10 In this context, ʾAbū al-Walīd Muḥammad ibn ʾAḥmad ibn Rushd (Averroes, 1125– 1198), a reputed philosopher and medical scholar who was the Grand Qāḍi (Chief Magistrate) of Cordova and a well-known authority on Islamic jurisprudence in the whole Muslim world then, and up until now,11 stated that “man ishtaghala bi ʿilm al tashrīḥ izdāda ‘imānan billāh” (“anyone who practices the science of dissection will increase [his] faith in God”).12 Moreover, the word ishtaghala in this statement also has significance and special connotations, as it means “practice” or “become occupied with” rather than denoting a simple theoretical knowledge of anatomy. In confirmation of this, Abū Bakr Muḥammad ibn Zakariyyā al-Rāzī (Rhazes, 854–925), in his book al-Manṣūrī, describes compounds to preserve cadavers. Thus, the practice of dissection for medical teaching in the Muslim world was not prohibited by the religion of Islam.
Ibn Zuhr described two forms of serious and fatal diseases that may affect the heart. One of them he described as follows: “In the heart, a watery fluid collection looking like urine, may occur. It is found enclosed and contained within its covering”.13,14 For the other disease he described “solid substances accumulating on the inside of the heart’s covering looking like layers upon layers of membranes”.15 It seems from these two descriptions that Ibn Zuhr was, most probably, describing the morbid changes in the serous and fibrinous forms of pericarditis. Thus, postmortem dissection to identify the cause and course of fatal diseases seems to have been known and acknowledged in his time. In confirmation of this, Ibn Zuhr, in his search for treatment for ulcerative diseases of the lungs, stated that “remedies for lung ulcerations are around in nature but are yet unknown to us, as sheep, when caught with a lung disease, do leave the herd, as shepherds say, and wander about as if looking for a plant to eat, and when they finish eating it their illness is relieved completely and they are back to normal”. Then, to confirm its cure, Ibn Zuhr said: “I did inspect lungs of sheep with the evident effect of breach of continuity and with obvious evidence of healing and union”. Hence, he resorted to postmortem examination of sheep in order to confirm his observation, although he could not identify the herb.16
The medical scholars of the medieval Islamic era, particularly from the time of al-Rāzī onwards, critically appraised the views of those who came before them in the light of their own experience, experimentation and direct observations from their practice of human dissection. This led to the correction of some ancient anatomical data, as will be shown in the following examples.
Contrary to Galen, al-Rāzī’s descriptions of the sacrum (ʿaẓm al-ʿajuz) and coccyx (ʿaẓm al-ʿuṣʿuṣ) are more accurate, as he described the sacrum as consisting of only three parts and stated that they look like vertebrae. Also, he described the coccyx as a separate bone, similarly consisting of three parts, with only the last part looking like a cartilaginous bone.17 Furthermore, Ibn Sīnā described the parts of the sacrum as “vertebrae with the strongest construction, most tight joints and widest wings”. Meanwhile, he recognised the independent nature of the coccyx as separate from the sacrum and, unlike al-Razi, he described it as consisting of three cartilaginous bones.18 Therefore, later Muslim scholars such as al-Zahrāwī, Amīn al- Dawlah Abū al-Faraj ibn Yaʿqūb ibn Isḥāq Ibn al-Quff (1233–1286), and Ibn al-Nafīs directly included the sacral and coccygeal vertebrae in the total count of the bones of the spine making them a total of thirty.19,20,21
Galen’s concept of the lateral movement of the head in both directions and forward and backward movements (nodding), although it had been accepted by ʿAlī ibn al- ʿAbbās (Haly Abbas, d. 982–994), Ibn Sīnā and other Muslim scholars, was criticised by Ibn al-Nafīs in his commentary on the anatomy of Ibn Sīnā’s Canon of Medicine.22,23,24
Furthermore, contrary to Galen’s description of the body of the lower jaw, the 12th-century Muwaffaq al- Dīn ʿAbd al-Laṭīf al-Baghdādī (1162–1231) confirmed the unitary nature of the lower jaw by experimentation in order to check the validity of his predecessor’s knowledge. The detailed description of this pioneering anatomical experiment is hereby translated from his book Kitāb al-ʿIfādah wa-al-‘Iʿtibār ( Book of Utility and Verification):
with regard to the shape, proportion and relations of bones and joints in a large number of the examined human skeletons, we have gained knowledge that we could not obtain from books, either because of being overlooked or because of lack of textual clarity or because our findings are different from what is written in those books, though indeed, direct observation is stronger evidence than hearing. Although Galen possessed the highest qualities in checking and verifying what he reports, direct observation is a more true source of knowledge than his reports. Then, an attempt can be made, if possible, to think of an explanation for his views. Among those discrepancies is the lower jaw bone, which all agreed with Galen to describe as consisting of two separate bones joined at the chin by a strong joint… However, based on our own observations, this organ (mandible) is, first and foremost, one bone only without a joint or a symphysis. Using various methods of testing, we examined it repeatedly as many times – as willed by Allah – in many specimens whose number exceeded two thousand skulls; but from all aspects, we did not find it except as a single bone. We also arranged the assistance of a distinct group, who examined it (the mandible) in our presence and then in our absence. They did not add anything to our observations and reporting. (Figure 4)25,26
Thus, the large number of the examined specimens also reflects his awareness of the statistical importance of the sample size in determining the significance of findings. Moreover, in order to avoid any possibility of bias, Muwaffaq al-Dīn al-Baghdādi repeated his experiment three times; first on his own, then together with a group of scholars and finally through another group of scholars on their own, so, to achieve accuracy of results, he utilised more than one method of testing.
Likewise, Ibn Sīnā, in the course of his study of moisture in various organs of the body, including bones, described the following experiment: “Take two equal-weight amounts of bone and hair, then distil them in the alembic. This results in more moisture and fat leftover from the bones with a less weight residue than that of the hair”. Thus, he concluded that “bones are more humid than hair”.27
Contrary to Galen, Ibn Zuhr permitted a form of sensation for both bones and teeth, though of a better kind in the latter. He stated that as bones, in a living body, grow and do not decay, although there is no hairlike branching of veins and arteries in them, so, they can, similarly, have sensation, although the nerve does not branch like hairs inside them. Ibn Zuhr then said that: “This is what I thought based on analogy and logical deduction”. He pointed out that the real answer to this matter is to verify it by dissection, which he did not do.28
Though Ibn Sīnā stated that the heart is located in the centre of the thorax and slightly tilted to the left, all other scholars, contrary to Galen, stated that, though the heart is in the centre of the thoracic cavity, its apex is directed to the left side. Ibn Sīnā, as well as all the scholars, agreed with Galen that the heart has two ventricles: the right containing thick blood, and the left containing thin blood. However, in addition, Ibn Sīnā described the third ventricle as a storehouse for the nutriments of the heart,29 which was refuted by Ibn al-Nafīs.30 In the medieval Islamic era, all the scholars before Ibn al-Nafīs, namely, al-Rāzī, ʿAlī ibn al-ʿAbbās, al-Zahrāwī and Ibn Rushd, agreed with Galen’s statement that the two ventricles of the heart are communicated through the interventricular septum by invisible pores.31,32,33,34 However, Ibn al-Nafīs stated that: “There is no connecting passage in between the two cavities because the heart substance there is compact without any obvious passage, as thought by some, or invisible passage that could transmit that blood as thought by Galen. Indeed the texture of the heart there is compact and its substance thick”.35
Contrary to Galen, ʿAlī ibn al-ʿAbbās confined the pulsations only to the arteries and introduced the names “al-ʿUrūq al-Ḍawārib” (pulsating vessels) for the arteries and “al-ʿUrūq Ghair al-Ḍawārib” (non-pulsating vessels) for the veins, thus highlighting the difference between arteries and veins.36 With the name “al-ʿUrūq Ghair al-Ḍawārib”, sometimes replaced by “al-ʿUrūq al-Sawākin (the motionless vessels), this nomenclature continued in the works of most of the scholars who came after ʿAli ibn al-ʿAbbās.
Also unlike Galen, all the scholars al-Rāzī, ʿAlī ibn al-ʿAbbās, al-Zahrāwī, Ibn Sīnā, Ibn Rushd and Ibn al-Nafīs described the arteries to the heart in more detail. They stated that two arteries emerge from the aorta at its beginning, the large one circulates around the head of the heart along with the vein and divides into branches which penetrate its substance, whereas the smaller one turns right, penetrates and divides within the substance of the right ventricle.37,38,39,40,41
Furthermore, Ibn al-Nāfīs, in his description of the attachment of the artery-like veins (pulmonary veins) to the heart, stated that: “The growing out of these two artery-like veins (pulmonary veins) is not from the left ventricle al-tajwīf al-aysar but from the structure ‘al-jurm’ that lies between the two ventricles of the heart, though they are inclined towards the left ventricle so that their cavities connect obliquely, with its cavity as if the direction of outlet of that cavity is slightly deflected to the right so that it continues with their lumens”.42 Thus, his description may, possibly, denote an early description of the left atrium.
Al-Rāzī, al-Zahrāwī, Ibn Sīnā, al-Baghdādī, Ibn al-Nafīs and Ibn al-Quff agreed with Galen that the ureters run obliquely for some distance in the bladder wall before opening into its cavity. Only al-Zahrāwī denoted that their course within the bladder wall is sinuous rather than straight. However, all of them, unlike Galen, identified the differentiation of the bladder wall into two layers with the ureters acquiring their course in between them, first by penetrating the outer layer then, near the bladder neck, penetrating the second layer to open into the lumen of the bladder. Meanwhile, Ibn al-Quff stated that the two penetration sites are not opposite each other and, as denoted by Ibn al-Nafīs, the first penetration is situated at a level superior to the second one.43,44,45,46,47,48,49
ʿAlī ibn al-ʿAbbās and Ibn Sīnā followed the statement of Galen, that “the canal of the stomach (the oesophagus) is carried upon the first four vertebrae of the thorax and lies on the right side of the remaining eight”.50,51,52 Thus, according to Ibn al-Nafis, it became popular among physicians to think that the oesophagus, after piercing the diaphragm at the twelfth thoracic vertebra, gradually widens to make the so-called “mouth of the stomach” as a receiving channel. However, Ibn al-Nafīs believed that this was a common erroneous conception and that the mouth of the stomach must be at a higher level, which is about the lower end of the sternum. Consequently, when it is subjected to disease, excessive amounts of the thin yellow bile, thick black bile or even over-feeding with a heavy meal, heartburn, which is a sharp pain at the mouth of the stomach, is felt behind the xiphoid process (al-Ghudrūf al-Khinjarī) at the lower end of the sternum. Also, the twelfth thoracic vertebra is the last thoracic one that joins the lumbar vertebra and gives rise to the last shortest rib. Hence, it is impossible for the mouth of the stomach to be located there, as it is very much lower than the lower end of the sternum, and the stomach will be opposite the lumbar vertebrae where the kidneys and the uterus are located. Hence, most of the small intestine will be above the umbilicus and higher up than the stomach, while we all know that the intestine is below or lower down than the stomach. Furthermore, it is known that the liver and spleen are on the right and left sides of the stomach, respectively, with the spleen being at a lower level than the liver. So, in the case of swelling in their convex regions the liver will be felt along the right costal margin (alsharāsif al-yumnā), and the spleen along the left costal margin (al-sharāsif al-yusrā), which confirms that the location of the stomach is in between them and above the umbilicus.53 Accordingly, Ibn al-Nafīs stated that: “The expected location of the stomach in the lower abdomen, according to their concept with most of the small intestine at a higher position to it, seems ridiculous and wrong”.
Therefore, by using analogical reasoning from some anatomical and pathological data, Ibn al-Nafīs was able to confirm his correct conclusion as regards the location of the stomach, which is close to our uptodate knowledge.
The presence of anatomical drawings within the medical textbooks was a trend that flourished in the Islamic era, reflecting an awareness of its educational role. During the whole of the Islamic era, with the increase in practical experience, the illustration of anatomical findings continued to progress in terms of quality and fine details. So, simple line-drawings illustrating the ventricles of the brain appeared in Kitāb al-Manṣūrī fī al-Ṭibb (Figure 7); also the cranial sutures in the Kāmil al-Ṣināʿah al-Ṭibbiyyah of ʿAlī ibn al-ʿAbbās al-Majūsī (Figure 8) and the al-Qānūn fī al-Ṭibb (The Canon of Medicine) of Ibn Sīnā (Figure 9); and the al-Mukhtar book of Muhadhdhab al-Din al-Baghdādī (Figure 10), who also made a diagram for the male urethra to illustrate its tortuous course (Figure 11).54,55,56,57,58
Later on, more sophisticated anatomical illustrations were made, as in the diagram for the maxillary sutures in Ibn al-Nafīs’ Sharḥ Tashrīḥ al-Qānūn (Figure 12). The schematic shape of the
bone as a triangle is to demonstrate its broad base (alveolar part) and the junction with the zygomatic bone which is longer than the frontal bone junction. In the diagram, schematic lines (1) represent the right and left maxilla zygomatic sutures and lateral boundaries of the maxillary bones; the apex (2) represents the suture with frontal bone; schematic line (3) represents the intermaxillary suture, which, according to him, is different from the midline suture in the hard palate (interpalatine suture); schematic line (4) represents the medial border of the maxillary bone; schematic line (5) represents the upper jaw teeth line. This diagram was embedded within his text.59
Moreover, the earliest known figures illustrating the anatomy of the eye appear in the Book of the Ten Treatises on the Eye of Abū Zayd Ḥunayn ibn Isḥāq (Johannitius, 809–873). Far more detailed, though less famous diagrams for the anatomy of the eye are found in the Kitāb al-Kulliyyat (Colliget) of Ibn Rushd (Figure 13). It shows a transverse section of the layers of the eye as circles within each other, and in the centre is the lens. In front of the transverse dotted line, the layers from the outside inwards are: cornea, aqueous humour, iris, aqueous humour. Behind the dotted transverse line from the outside inwards are the following layers: the sclera, the choroid, the retina, the vitreous humour. To each eye is attached an optic nerve which joins the other at the optic chiasma without crossing (in agreement with Galen), and then proceeds and joins the brain.60
In the Kitāb al–Manāẓir of Ibn al-Haytham, he showed the layers of the eye represented by circles following each other to demonstrate how a straight line of light entering the eye through the centre of the cornea passes through the centre of the iris and comes in contact with the centre of the lens, then to the centre of the optic nerve, proving that the centres of all the layers are along one straight line (Figure 14).61
Next is the diagram illustrating the brain, the two hollow nerves (optic nerves) and their cruciate crossing (optic chiasm), and illustrating the eye by showing its layers and humour. And I write on the humours their names and on each layer the letter ‘Ṭ’ [first letter of the Arabic word ṭabaqah meaning layer] to indicate it as a layer plus the first two letters of its name to identiy it, wa-Billāh al-tawfīq.”
However, the most refined medieval diagrammatic rendering of the anatomy of the eye yet discovered, is that made by the 13th-century Khalīfah ibn Abī al-Maḥāsin al-Ḥalabī (Figure 15) in his book al-Kāfī fī al-Kuḥl (The Book of Sufficient Knowledge in Ophthalmology), completed not long after the year 1256. In the Introduction to this book, after listing the content of its first part dealing with the anatomy of the eye and eye diseases, al-Ḥalabī states: “Thereafter, I will illustrate the brain, both eyes and both their nerves by a diagram as best approximating as is possible for me to do”. Then, in what may be described as a legend to the above-mentioned illustration located at the end of Part I of the book, he says:
This is followed by a full description of all the structures shown in the diagram with an apologetic note at the end, saying that “They were represented as far as can be done on the flat rather than the spherical plane.”62,63
So, in this time-honoured diagram that may well be based on drawings dating at least as far back as 1000 years, we get an insight into a modest attempt to represent what W.D. Sommering so luminously portrayed in his classic illustration ‘Table 1, in Horizontal Section Through Human and Animal Eyes’ in Göttingen in 1827.64
Another remarkable step in the evolution of anatomical illustrations during the medieval Islamic era, was whole body diagrams made by the 14th-century Manṣūr ibn Muḥammad ibn Aḥmad ibn Yūsuf Ibn Ilyās (fl. around 1390) in his book Tashrīḥ-i badan-i insān (The Anatomy of the Human Body). The treatise, in Persian, consists of an introduction followed by five chapters on the five systems of the body: bones, nerves, muscles, veins, and arteries, each illustrated with a full-page whole-body anatomical diagram. The whole-body drawing shown in Figure 16 was used by Manṣūr to illustrate the veins of the body, but it also shows the viscera including the digestive systems with the liver and also the spleen. In addition to the veins, the labelling, in Arabic and Persian, includes the duodenum al-ithna ʿashar, the jejunum al-ṣa’im, the Ileum daqīq, the appendix ‘a’war, the colon qawlūn and the rectum mustaqīm. But the drawing in Figure 17 illustrates the arteries of the body, and includes the viscera, but only shows the labelling for the arteries. Mansur’s reputed anatomical illustration of a pregnant woman (Figure 18) is essentially his arterial figure on which a gravid uterus, with the foetus in a breech or transverse position, has been superimposed. According to Khalili et al., the fact that Manṣūr selected a drawing of arteries to demonstrate a gravid uterus may indirectly indicate that he regarded the fetoplacental unit as a part of the circulation.65,66
Chronologically, the next famous gravid-uterus anatomical drawing was sketched a hundred years later by Leonardo da Vinci (1452–1519). Da Vinci’s drawing is obviously more sophisticated, realistic and artistic; however, it still shows the foetus in a breech presentation (Figure 19).
Therefore, the whole body anatomical diagrams of the 14th century Manṣūr Ibn Ilyās represent a step in the further evolution of anatomical drawings, a step that preceded the famous magnificent whole-body drawings of the 16th century Vesalius in his reputed De Fabrica Humanis Corporis.
The functional anatomy of the human body was also one of the sciences very much appreciated by the medieval Islamic scholars as it revealed to them the perfection of the Creator. Al-Rāzī in his al-Manṣūrī, Ibn Sīnā in his Canon, and al-Zahrāwī in the first Maqālah of al-Taṣrīf, discussed physiology together with the anatomy of each organ or group of organs (Figure 20),67,68,69 while Muhadhdhab al-Dīn al- Baghdādī in his al-Mukhtār and Ibn Zuhr with his co-author Ibn Rushd in the Kulliyyat (Colliget) devoted an independent chapter to it.70,71 Meanwhile, Ibn al-Nafīs, in addition to his critical commentary of the anatomy and physiology of Ibn Sīnā in Sharḥ Tashrīḥ al-Qānūn, also authored an independent treatise on physiology, entitled Risalat al-ʿAʿḍāʾ (The Treatise of Organs).72,73
Moreover, the knowledge about human physiology was equally valued and admired by the general public, as it was included in many religious guidance and health-education books addressed to them. An example of this genre is Kitāb Ṣayd al-Khātir, authored by Ibn al-Jawzī (1114–1200) in three volumes containing aphorisms and wise counsels that includes general knowledge about human physiology, describing functions such as digestion, respiration and reproduction in a simple but varied and eloquent style.
The following are some examples of the critique and originality developed in human physiology as the result of the use of the inductive method in scientific research by scholars in the medieval Islamic era (discussed in Chapter 3), and its impact on ancient physiological theories and concepts.
As regards physiological concepts, medieval Islamic scholars accepted only what is proven right by their own experiments. So, before Ibn al-Haytham, the Galenic (extramission) theory of vision raised wide controversy among scholars since al-Kindī (805–873) was a staunch supporter of this theory, Abū Bakr al-Rāzī rejected it, and his treatise Kitāb fī Kayfiyyat al-ʿIbṣār (The Book on the Method of Vision), as documented by Ibn Abī Uṣaibiʿa, was authored to show that vision does not occur by the emanation of rays from the eye.74,75 In addition, in his Kitab al-Manṣūrī (Liber ad Almansorem), al-Rāzī stated that the pupil contracts or dilates according to the amount of light required by the crystalline humour, which is in contrast to Ḥunayn (as Galen, who stated that the pupil is dilated by the pressure of the emerging visual spirit (pneuma).76 Furthermore, in the book al-Mabāḥith al-Mashriqiyyah by Fakhr al-Dīn al- Rāzī, who was also an opponent of Galen’s visual-ray hypothesis, it is stated that “Muhammad ibn Zakariyya denied the presence of a source of light in the human body, as light cannot be found except in fire or stars. Also, dense bodies and their insides are bound to be dark, so, how could the brain with its thick coverings be a light-emitting body?”77,78
It is of interest that Ibn Sīnā did not include his detailed refutation of the extramission (visual-ray) theory of vision in the ophthalmology section of his medical encyclopedia, The Canon of Medicine. In that book, in the course of discussing the diseases of the eye and the abnormalities of eyesight, he mentioned the two theories, extramission (Galen) and intromission (Democritus, c. 460–370 BCE), only by their names, then wrote: “Which of those two views is correct is left for the philosophers, not the physicians, to evaluate”.79,80
However, in the al-Kulliyyāt fī l-Ṭibb (Colliget), in the section on the functional anatomy of the eye, Abū al-Walīd Muḥammad Ibn Rushd (1126–1198) stated that: “Vision is, certainly, not due to something that emanates from the eye, as beheld by Galen; but the eye receives the color by the clear structures inside it, as in the case of a mirror”.81
Furthermore, the 13th century Ibn al-Nafīs had his doubts about the Galenic concept that the crystalline humour communicates, through the iris, with the object to be perceived, as in his book Sharḥ Tashrīḥ al Qānūn he stated that: “The form of the visible objects does not fall and impress on the glacial humour (crystalline humour, lens)”. In addition, he said:
In our opinion, the need for the humours of the eye (the albuminous or aqueous, the crystalline and the vitreous) is not for the forms to fall and impress on any of them, but to render the inside of the eye humid enough so that its temperament becomes close to that of the brain; thus, when the visual spirit (pneuma) enters into the eye, it will not undergo a change in temperament.”82,83
Finally, the controversy was brought to an end by Abū ʿAlī al-Ḥasan Ibn al-Haytham (Latinised as Alhazen or Alhacen, c. 965–c. 1040), a physicist, astronomer, mathematician and philosopher, who positively criticised this theory and set out to construct a counter-theory by an entirely new approach and methodology, through the experimental study of the physics of light and vision. He showed that what is really sensed is not the object itself, but a punctuate optical image due to light reflected from its surface to the eye, then serial re-projection of the punctuate image in the eye, optic chiasma and brain. So, as Lindberg stated, “Ibn al Haytham created a new optical tradition and established the aims and criteria of optics which would prevail”.
Also his establishment of punctiform analysis of the visible object and the need for one to one correspondence between points in the visual field and points in the eye as permanent and essential elements of his theory thus providing the basic framework that has prevailed until the present.”84
Hence Ibn al-Haytham was acclaimed in both the East and West as the founder of modern optics by virtue of his seminal work, Kitāb al-Manāẓir.
All the medical scholars in the Islamic era, as well as Ibn al-Nafīs, followed the description of the pulmonary vessels by Galen and his predecessors, and agreed with Galen that man and all animals which have lungs have a right ventricle, too, which Galen described as “a common passage or a cistern, so to speak, in which one vessel with a single tunic is inserted into it and another with double tunics issues from it, and the blood is attracted to it through one of the vessels and expelled from it through the other”.85,86 Meanwhile, they as well as Galen believed that the right ventricle is necessary for the thinning and warming of the incoming blood to the heart, as according to Ibn al-Nafīs only, if air gets mixed with the blood while it is still thick, the resulting mix will not be of homogenous particles.87 Also, they admitted that the vital role of the heart is the formation of the vital pneuma in the left ventricle and its distribution all over the body by the arteries. This pneuma is thin, light, and mobile, as it is formed from the thinnest blood which is well mixed with the attenuated air (pneuma), hence in the left ventricle, according to Ibn al-Nafīs, there must be present attenuated air (pneuma) and very thin blood, so that vital pneuma could be formed from their mixture.88,89,90 So, all the medical scholars before Ibn al-Nafīs agreed with Galen that the attenuated air (pneuma) might flow easily into the heart, attracting it during the diastole, and followed his assumption that the two ventricles are connected through invisible pores in the interventricular septum, and a considerable amount of blood is taken over through it from the right to the left ventricle.91,92,93,94
However, Ibn al-Nafīs proved anatomically that, in the interventricular septum, there are no pores, whether visible or invisible, as it is not porous but compact, even more than any other part, and there is no communication between the two ventricles at all.95 Therefore, contrary to Galen, Ibn al-Nafīs believed that all the attenuated blood in the right ventricle must be expelled through the arterial vein (pulmonary artery) and its branches into the lung substance which fill the spaces at the division of the vessels and concocts the outer air filling it.96 Meanwhile, the thick-walled arterial vein (pulmonary artery) and its branches permit only the thinnest blood to filter out into the substance of the lung. Hence, this filtrate gets mixed with a large amount of previously attenuated air in the lung spaces. Then, the formed mixture must be concocted in the lung until it becomes thin spirituous blood which is suitable for the formation of the vital pneuma in the left ventricle of the heart.97 In addition, unlike Galen, Ibn al-Nafīs believed that a simple element like the attenuated air (pneuma) on its own was not eligible as nutriment, but when well mixed and concocted with the thinnest, warm, blood and forming the hot, thin, spirituous blood, then it becomes suitable nutriment for the nourishment of the vital pneuma in the left ventricle of the heart.98,99 Hence, according to Ibn al-Nafīs, the thin, warm and spirituous blood formed in the substance of the lung penetrates easily into the thin-walled venous arteries (pulmonary veins) through its terminal pores to reach the left ventricle of the heart to nourish the vital pneuma.100 Therefore, according to him, the blood in the left ventricle comes from the lung and not from the right ventricle, as was believed by Galen.
Furthermore, Ibn al-Nafīs believed that, originally, the left ventricle was not suitable for the formation of the thin spirituous blood which is necessary for the nourishment of the vital pneuma, as the heart is in continuous movement of systole and diastole, which will not allow for the required time needed for the effective mixing and concocting of the attenuated air with the hot thinnest blood. Furthermore, the alternative and more suitable place for the mixing and concocting of that mixture should have plenty of attenuated air. Therefore, the lung, in addition to being near to the heart, represents the most suitable place for this process to take place.101
On the other hand, Ibn al-Nafīs suggested that the thin spirituous blood does not, instead, penetrate the terminal ends of the rough arteries in the lung (branches of the windpipe), not because of their naturally nicely proportioned size, which permits vapour and air but remains impassable to blood and other thick substances, unless they loose their natural adjustment of size in the case of wounds or diseases, as was suggested by Galen, but rather due to a retentive faculty present in the lung that holds on to what is beneficial and expels what is harmful to it.102,103
Also, according to Ibn al-Nafīs, what is left in the branches of the arterial vein (pulmonary artery) is the thicker part of its blood. It will come out from its terminal pores and is consumed for the nourishment of the lung substance.104 Thus, he contradicts Galen’s assumption that the nourishment of the lung must be basically by thin spirituous blood coming to it from the heart through the venous arteries (pulmonary veins). Ibn al-Nafīs stated that this thin spirituous blood is not suitable for its nourishment because the lung substance is not so thin that it needs such blood. On the contrary, it is fleshy and humid, hence its nourishment should be of watery rather than spirituous blood.105
Therefore, according to Ibn al-Nafīs, the venous arteries (pulmonary veins) contain thin spirituous blood coming to them only from the lung and not from the heart. However, in agreement with Galen, he stated that during the contraction of the heart, all that is sooty and fuliginous is poured off through the venous arteries (pulmonary veins) to return to the lung to be expelled in the expiration.106
Furthermore, while Galen considered that the arteries accompanying the veins of the heart are for cooling it, Ibn al-Nafīs considered them to supply the vital pneuma to all its parts, except the left ventricle and interventricular septum, because of their direct contact with it.107
Therefore, the above-mentioned physiological concept of the circulation of blood from the right ventricle to the lungs and then to the left ventricle, based on the anatomical fact that the interventricular septum is not porous, made Ibn al-Nafīs the greatest physiologist of the medieval Islamic era.
Ibn Abi Uṣaibiʿa reported that Aḥmad ibn Abī al- Ashʿath (d. c. 975), in his book al-Ghadhī and al- Mughtadhī (The Nourisher and the Nourished), gave the following description of an experiment:
“It should be noted that food, when entering the stomach in a great quantity, causes it to expand and its folds to stretch, as I observed in the case of a “sabuʿ”(a wolf and the like), which I dissected alive in the presence of the Emir al-Ghadnafr (Governor of Mosul, d. 978). One of those present believed its stomach to be small, and so I started to pour water into its mouth. We poured one jug after another, until we counted what equalled in amount to around forty “ruṭl” (equivalent to 18 litres). I then looked at the inner layer of the stomach and found that it had stretched until its surface became smooth with a flatness not less than that of the external layer. Then, I cut it (the stomach) open and when it shrank (contracted) after all the water had come out, the roughness of the inner layer returned. During all this, the “al ‘bawwāb” (pylorus), God is my witness, did not let go.”108
Furthermore, Fakhr al-Dīn al-Rāzī, a polymath who was a reputed authority in Qur’ānic studies and the principles of jurisprudence, an eminent physician and a philosopher, described another animal experiment in his book al-Mabāḥith al-Mashriqiyyah. In the course of discussing the action of the retentive faculty of the stomach in tightly containing and directly contacting the food from all sides regardless of how full it is, he stated:
“And the evidence for the presence of this faculty in the stomach is that we can see with our own eyes that if we give an animal a moist meal like drinks or soft food, then incise his tummy at that time, we will find the stomach containing it, surrounding it from all sides and the “Bawwāb” (the pylorus) contracted so that nothing of that soft meal could by any means seep out.”109
Al-Rāzī, Ibn Sīnā and al-Zahrāwī, for the attraction of the useful chyle from the intestine by the mesenteric veins, followed the Galenic assumption that “Actually, the coils of the intestine have countless veins from the liver inserted into them”, so, “Certainly every particle of the nutriment is forced to encounter the mouth of a vessel at some point” and “In fact, the whole curved surface of the intestine is pierced by innumerable openings that extend to the inside and seize upon the useful part of the nutriment as it is going by”.110,111,112,113 However, Ibn al-Nafīs refuted this assumption. Meanwhile, he considered it as “one of the wide spread myths”, as the nutriment in the intestine is very humid, and by the heat of the nearby liver and gall bladder, vapours and winds may readily be produced from it. Hence, distension and even change of position in some of its parts may take place. Therefore, if, as was previously suggested, the mouth of the veins opens directly into the intestine, then they will also suffer from distension, which may be even worse due to their thin walls, as it may lead to their tearing off and subsequent serious bodily damages.114
Thus, Ibn al-Nafīs suggested a new hypothesis instead, and stated that:
“Therefore, the lining of the intestine must be of wide pores, so that filtration (“rashḥ”) of the useful chyle outside of its lumen could take place easily. Then the withdrawal of this filtrate (useful chyle) to the veins takes place partly by the attractive force of the liver itself and partly by the absorptive power (“‘intishāf”) in the veins themselves. Then it is sent up through the portal vein to the liver.”115
In fact, the hypothesis of Ibn al-Nafīs may be represented as the first step forward towards the understanding of the process of absorption from the intestine.
Furthermore, unlike Galen and all medical scholars in the medieval Islamic era, Ibn al-Nafīs considered the masariqa (mesenteric veins) rather than the liver to be the origin of the portal vein usul, as by them the nutriments are sent up from the intestine to the portal vein. Then, the portal vein gives rise to many branches in the different parts of the portal region of the liver to distribute the nutrients and enable its transformation into the blood and other essential materials.116
Hippocrates, Galen and all the medical scholars in the medieval Islamic era stated that water is necessary for the animal, as the chyle resulting from the food is mixed with it so that it can be taken up successfully from the stomach and intestine into the veins masariqa and then through the fine veins in the liver. Therefore, the blood in the vena cava which arises from the convex portion of the liver and leads to the upper and lower parts of the body is still charged in abundance with a thin watery fluid, which should no longer be retained in the body as it would become an alien burden to the veins. Hence, the kidneys purify the veins from the residue of their nutrition.117
On the other hand, Galen, contrary to all his predecessors, believed that arteries (including renal arteries) contained blood and that the kidneys purified this blood, as their arteries are so large and branching like the veins into the very cavities of the kidneys,118 although he did not explain the source of this watery residue in the arteries. However, Ibn Sīnā followed the suggestions of Galen, but explained the source of this water residue by describing how “these arteries (renal arteries) frequently attract impure blood from the stomach and intestine”.119
Ibn al-Nafīs refuted Ibn Sīnā’s claim, as “this is not the function of the arteries”. Meanwhile, he explained the source of water residue in the arteries as follows: “As the blood reaching the heart by the vena cava is originally watery, then becomes even more watery in the right ventricle after its thick portion is sent to the heart for its nourishment”. This watery blood satisfies the need of the heart in moving a large portion of it to the lung by the process of vaporization, which will be promoted by its content of plentiful water residue. Subsequently, out of this blood, a large portion will get mixed with the attenuated air in the lung spaces, forming the thin spirituous blood which is suitable for the nourishment of the vital pneuma in the left ventricle. Accordingly, the blood in the left ventricle and subsequently the arteries is associated with plenty of thin water vapour. The presence of this excessive water residue in the arteries makes their blood prone to infection and decomposition. Hence, its purification takes place in the kidneys.120
Therefore, in agreement with Galen, the kidneys themselves relieve the blood of its entire watery portion.121
Al-Rāzī, al-Zahrāwī, Ibn Sīnā, al-Baghdādī, Ibn al-Nafīs and Ibn al-Quff, considered the anatomical arrangement of the ureterovesical junction as an amazing urinary anti-reflux mechanism because the accumulation of urine within the bladder will lead to the approximation of the inner layer towards the outer layer until the two layers appear as if they were one layer leading to the tight closure of the portion of the ureter in between, thus preventing the backward return of urine to the kidneys122,123,124,125,126,127,128 (Figures 28 and 29).
However, contrary to the above-mentioned mechanism, for the explanation of the urinary antireflux, Galen relied on the oblique course of the ureters within the bladder wall and the presence of a covering in the inside part of the ureteric opening into the bladder “comparable to the lid (skyphon) of a dovecote (ureteric valve), which is not something different from the substance of the bladder, but part of it so clearly fitted to its form”. This valve thrusts inwards and opens up to allow urine in and outward to prevent it from refluxing (Figure 30).
As regards the mechanism of voluntary emptying of the bladder, al-Rāzī, al-Zahrāwī, Ibn Sīnā, al-Baghdādī, Ibn al-Nafīs and Ibn al-Quff agreed with Galen on the presence of transverse muscle fibres around the neck of the bladder acting as a sphincter (al-ʿaḍalah al-ʿāṣirah) to prevent the involuntary passing of urine.129,130,131,132,133,134,135,136 However, they disputed his view as regards its role in the voluntary act of emptying the bladder. All of them stated that: the fullness of the bladder, while the sphincter around its neck is contracted, leads to its distress and the subsequent inhibition of the sphincter to let the urine out, as according to Ibn Sīnā, the bladder is rich in nerves so as to increase its sensitivity.137 Hence, the inhibition of the sphincter is associated with simultaneous contraction of the bladder wall to help urine to be squeezed out (Figure 31).
However, Galen’s concept of the mechanism of voluntary emptying of the bladder was the exact opposite to that described by the physicians of the medieval Islamic era. He believed that the process starts by the relaxation of the already tensed bladder wall and the contraction of the abdominal muscles to help urine to be squeezed out. Meanwhile, the sphincter muscle simultaneously remains tensed so as to help the expulsion of urine through the bladder neck and the oblique urethra (Figure 32). Contrary to Galen and Ibn Sīnā,138 none of the above-mentioned physicians stated that contraction of the abdominal wall muscles is needed as part of the normal mechanism of the voluntary voiding of urine. Furthermore, al-Rāzī pointed out that this contraction of the abdominal wall muscles is called into action only if the urine is very little in amount or the bladder is weak.139
Thus, the ideas and findings of those Islamic physicians as regards the anti-reflux and micturition mechanisms conform well with our present-day concepts.140,141,142,143
The word “rūḥ” frequently met in all medieval Islamic writings, is a purely physiological term widely used to identify a special faculty or force of action in the human body without any theological or logical connotation whatsoever. In confirmation of this, Ibn Zuhr, in his encyclopaedic work al-Taysīr, clarified this, writing:
By saying “rūḥ”, I do mean that thing with which vision occurs as if it is “Nūr”(an illumination), also, in some other places, I use it to mean “an airy thing that became thinned”. This is what physicians mean when they talk about a spirit; they do not mean what is understood from it by the logicians. I made this clarification in order to avoid any misunderstanding caused by shared names.144
In another place in his book, Ibn Zuhr wrote: “When I say: Nafs, I only mean the force (faculty) that is present as an effect of the ‘nafs’.145 Ibn al-Nafīs also wrote a similar clarification of the term “rūḥ” and other terms used at the end of his book Sharḥ Tashrīḥ al-Qānūn.146