Examining The Accuracy of The Earliest Anatomical Discoveries

Throughout history, the discovery of anatomy through the process of dissection has always elicited curiosity in numerous scholars scattered through the empires of the world. Of interest is how dissection was incorporated in the study of Medicine as a science and how this was swayed by culture, religion and the established beliefs of specific historical periods. The correlation between the process of dissection and the study of anatomy was initially incidentally linked and its popularity as a science fluctuated throughout different periods of history.

In this report, I would like to examine the accuracy of some of the earliest anatomical discoveries during the pre-medieval period, based on theories developed by scholars such as Hippocrates, Herophilus and Erasistratus who delved into the study of anatomy through cadaveric dissection to different extents and how this influenced the accuracy of their studies. I would especially like to analyse Galen's contribution and legacy to medicine and the study of anatomy, highlighting how his deviation from human cadaveric dissection affected the vast inheritance of his work. I will conclude with how the study of human cadaveric dissection at the core of anatomical and medical studies, led to the most important anatomical discoveries which were able to advance the field of medicine towards the full integration of dissection in the modern medical curriculum. The Early History of Anatomy Between the Greek and Anatolian peninsulas in 460 B.C. Hippocrates, the "Father of Medicine", was born (Persaud, 1984).

Although very little of his anatomical studies were correct, seeing as he based the physiology of the human body on the concept of four "humours" (Porter, 2017), Hippocrates was the first to remove magic and superstition from Medicine and establish it as a science. It is unknown whether he carried out human cadaveric dissection as it was considered an "unpleasant if not cruel task" (Persaud, 1984) although he most likely observed wounds and carried out animal dissections, which allowed him to identify several organs such as the lungs, kidneys, urinary bladder and the bowel (Persaud, 1984). His most substantial anatomical errors were his more detailed descriptions of the cardiovascular system and the function of the auricles of the heart as reservoirs of air (Persaud, 1984).

Nonetheless, Hippocratic physicians practiced patient-centred care and were keen observers of patterns in pathology, skills which modern medics aspire to gain and which institutions such as universities and the General Medical Council (GMC) are ensuring are included in the modern curriculum for a Bachelor of Medicine and Bachelor of Surgery (MBBS) degree. In addition, Hippocrates established the concept of "do no harm" or non-maleficence, now a Principle of Medical Ethics (Porter, 2017).

Aristotle, born subsequently to Hippocrates' death, greatly contributed to the knowledge of anatomy albeit not being a physician and not having himself dissected a human cadaver (Crowther, 2018). He believed, as many scholars after him would, that human and animal anatomy was comparable (Persaud, 1984), however he was able to advance the structural presence of great vessels such as the aorta and the pulmonary vein and that these arose from the heart and not from the brain, as previously believed. His description of the trachea with cartilaginous rings was correct, including its positional relationship with the oesophagus and the function of the epiglottis during food ingestion. Aristotle described the GI tract accurately, correctly described the porta hepatis through the liver although without identifying the connection between the hepatic artery and the coeliac trunk, the first major branch of the abdominal aorta (Abdel-Misih and Bloomston, 2018). His description of the function of the kidneys as the organ of separation and excretion was correct although his view of the structure of the kidney as made up of numerous small kidneys (the pyramids) was perhaps a bit simplistic (Wallace, 1998). After the fall of Greece to the Roman Empire, scholars of literature and science retreated to Alexandria, the intellectual and cultural centre of the world. The rigidity of Aristotelian scholars was overruled by scholars who favoured a more empirical method of study which included scientific investigations, observations and clinical histories. Two prolific individuals during this period were Herophilus of Alexandria and Erasistratus of Ceos, the former considered to be the founder of systemic anatomy whilst the latter the first scientific physiologist (Dobson, 1925).

As contemporaries and scholars in similar fields of Medicine using the vital tool of cadaveric dissection, their collaboration led to an overall development in the knowledge of anatomy. In Alexandria, cadaveric dissection was forefront for understanding human anatomy and both Herophilus and Erasistratus were accredited with human vivisection on criminals as well as the removal of live foetuses from the womb.

Herophilus advanced from Aristotle, by providing a description of at least seven pairs of cranial nerves (von Staden, 1992) and understanding that as they emerged from the brain (Porter, 2017), this proved the brain to be the seat of human intelligence, as opposed to the heart. Although antecedent to Galen, Herophilus also suggested that there could be more than seven cranial nerves (Persaud, 1984). Galen had advanced on this and recognised the importance of tracing the source of all nerves via dissection, which Herophilus had not done. Herophilus and Erasistratus disagreed over the content of the blood which Herophilus correctly maintained was blood whilst Erasistratus suggested was pneuma (Porter, 2017).

Erasistratus was also credited with individual anatomical discoveries which included the function of the bicameral heart as a mechanical pump and illustrated the function of the heart valves, which had been discovered by Herophilus (von Staden, 1992). The freedom of their studies of anatomy through dissection and vivisection allowed the medical school of Alexandria to further thrive and attract more scholars as their often accurate and empirical findings were repeatable by others who were keen to gain a truthful understanding of human anatomy. Therefore, the discoveries accredited to them are found in the works of succeeding eminent scholars such as Galen as unfortunately all of their written works were lost.

Despite the permeating religious and moral impediment, Herophilus and Erasistratus built the foundations of the study of anatomy on dissection, as previously this was limited to a superficial exploration of the human body triggered by pathological requirements rather than for academic purposes (Gosh, 2015).

The Roman conquest of Alexandria in 30 B.C. by Octavian, later called Augustus (The Metropolitan Museum of Art, 2000), followed the defeat of Marc Antony and Cleopatra on behalf of the emperor Julius Caesar. The conquering of modern-day Egypt meant that human cadaveric dissection was no longer permitted (Persaud, 1984). During the period of the Roman Empire which lasted until the invasion of the Sassanid Persians in 619 A.D. (The Metropolitan Museum of Art, 2000), the infamous scholar Claudius Galen was born. Galen is one of the most celebrated anatomists of antiquity due to his numerous, often public, dissections on different animal species which led to his extensive knowledge of anatomy allowing him to write numerous books on the subject.

Galen understood and highlighted to his students the importance of a thorough knowledge of anatomy for the physician. Being appointed as gladiator to the physician provided him with opportunities to observe human anatomy in vivo which he would not have otherwise been able to witness. However, this was not a problem for Galen, who considered the internal organs of the pig to be extremely similar to those of a human. What ensured Galen's popularity was that he explained the complexity and the exquisite relation between the structure and function of different parts of the human body as due to divine providence so was thus accepted by all religions and translated into many languages. Galen's studies focused on the dissection of the veins, arteries, muscles and nerves. His description of the human bones was one of the first that attempted to build an anatomical vocabulary.

Although Galen was very meticulous in his description of internal organs, his obstinacy in relying on animal dissections led to him committing numerous errors. The effect of Galen's legacy on future anatomists meant that his incorrect description of the circulation of blood and his adherence to the pneumatic theory established by Erasistratus whereby the arteries contained pneuma, delayed the discovery of the pulmonary and systemic circulation until the 17th century, when the circulation of blood was discovered by William Harvey.

The Hippocratic theory regarding the four "humours" of the body: blood, phlegm, black bile and yellow bile, was a theory supported by Galen and which described that a diseased state was caused by an imbalance of one of these fluids in the body. He thus practiced blood-letting, also known as venesection, to cool the body and return balance in the body. This practice would permeate until the nineteenth century as well as the theory of the "humours". I would argue that although Galen meticulously described many organs of the human body such as the female reproductive system, he partially retreated in so closely correlating philosophy and theology with medicine. He scorned many of his colleagues who based their studies on empirical findings but then prided himself as a medical scientist.

Famously, he publicly demonstrated that severing the spinal cord of a live pig at different levels would eventually cause the pig to stop squealing as eventually the recurrent laryngeal nerve was severed (Gross, 1998). This proved the extension of the spinal cord from the brain and that the brain controlled behaviour (Gross, 1998). However, his mistakes were based on his self-importance which shunned any variation from his works as well as his explanations of anatomy and physiology through speculations about the macrocosm instead of direct observation and empirical results. In 1315, the first ever recorded public human dissection was carried out in Bologna by Mondino de' Luzzi (Porter, 2017).

Anatomy would now become more and more principal in the study of medicine yet it was a while before anatomical theatres were built and anatomical dissection was included in the medical curriculum. Galen's anatomy pervaded and cadaveric dissection was justified as a way to reflect the perfection of the human body created by God rather than to advance clinical practice and surgery based on a more thorough and accurate knowledge of human anatomy.

Because of the papal ban by Boniface VIII against the dismembering of bodies in 1300 (Porter, 2017), the increasing occurrence of cadaveric dissections can be explained as a growing desire to establish the cause of death after a homicide through an autopsy, as well as using dissections as a form of punishment for criminals and at the same time provide entertainment and forewarning for citizens.

Although the religious injunctions prohibiting dissection during this period remained, it is arguable that public apprehension was decisive in ensuring that the practice of dissection was constrained to strict rulings (Gosh, 2015). However, it is unlikely that many scholars did use these opportunities to advance the study of anatomy as dissections had now simply become a ritual of demonstrating known material from Galenic texts which would have guided the student in their medical education rather than for discovery (Porter, 2017). A dissection was thus book-led with a praelector lecturing from a pulpit whilst a lowly aid dissected the cadaver, with the praelector blindly following the text with an indistinguishable view of the dissected body (Gosh, 2015). It is thus rational to conclude that the Middle Ages was thus a period of few anatomical discoveries.

In addition, it is an era from which we have the most simplistic anatomical illustrations in comparison for example, with the Renaissance period. It is important however to establish that the illustrations of the Middle Ages had a different role, that to simply represent general and not factual anatomy and as use as teaching aids (Porter, 2017). To whom we can accredit the most accurate anatomical illustrations is none other than Leonardo da Vinci, 1452-1519 (Heydenreich, 2017). Leonardo studied anatomy is the most complete of ways, from the perspective of a mathematician and from that of an artist.

Although Leonardo often relied on tradition rather than observation, for example in his description of the liver as five-lobed rather than four and remaining relatively faithful to Galen, his illustrations were certainly superior and more "realist" compared to those of medieval anatomists (Porter, 2017). Leonardo's illustrations convey a thorough understanding of the musculoskeletal system with no doubt on the exactness of the origin and insertion as well as a knowledge of the function of muscles and their antagonists and the complex action of muscles and bones acting as levers during dynamic movement.

As an advancement from Erasistratus, Leonardo discovered the movement of heart valves during systole and diastole and the nature of blood vessels and how these change with age (Keele, 1973). It is surprising that through his technically advanced experiments, Leonardo was unable to discover the circulation of blood. These successes could not have been achieved without the aid of the true science of dissection and a keen eye for observation Vesalius and Galenism. Overall, the formal study of anatomy through dissection in the great European universities such as Bologna and Paris stagnated until the beginning of the career of the scholar Andreas Vesalius, born in 1514 (Persaud, 1984). Lecturers of anatomy were often ignorant of anatomical nomenclature and faithfully followed Galenic texts, without accepting deviations from his work. Jacob Sylvius, a great influencer of Vesalius stated that "man must have changed his structure in the course of time, for the teaching of Galen cannot err".

However, the bright and enterprising Vesalius, took his medical education into his own hands, privately dissecting small animals and rodents for his own studies. In 1537, Vesalius received his Doctor of Medicine degree and was appointed Professor of Surgery at the University of Padua (Del Negro, 2003; Persaud, 1984). Vesalius was exceptional in the study of anatomy for his redefinition of the dissection, often encouraging his students to dissect whilst teaching and lecturing them as well as utilising comparative anatomy of small animals to accentuate specific features of the human body. During his professorship at the University, Vesalius correctly articulated a human skeleton and was the first to finally compare and bravely highlight the errors committed by Galen in his conclusions drawn by comparing the skeleton of an ape to that of a human (Persaud, 1984). Vesalius thus emphasised the necessity of cadaveric dissection to uncover the true anatomy of the human body and suggested that this was the reason behind Galen's many unfounded "discoveries". Vesalius returned the process of dissection previously known as an unfounded and distasteful science to a level of upmost importance, as the principal tool for pure scientific analysis in the field of medicine.

Clearly, Vesalius received brutal criticism from the supporters of Galen but he remained unfazed and unlike Galen, he accepted and often replied to constructive criticism from his fellow colleagues. Vesalius was not shy or unable to argue his case, as he paved way for a more dynamic advancement of the science of anatomy, identifying obvious errors in the work of previous scholars simply through scientific experimentation and observation of the human body. Vesalius' main impact was to move away from the concept that dissection was merely an addition to anatomical illustrations and to establish that dissection was essential to learn anatomy (Gosh, 2015). However, Vesalius did not disregard the work of previous scholars and when in 1543 he published De Humani Corporis Fabrica, 659 pages of illustrated anatomy, the book was divided in seven sections, following the Galenic approach to dissection. If his methodology for the process of dissection, illustrated in the text, was followed correctly, any aspiring student of anatomy could independently dissect and learn from a human cadaver.

Despite the more thorough study of anatomy on human cadavers, Vesalius' work was also entwined with a few incorrect details such as the presence of the "rete mirabile" at the base of the brain, the division of the sternum and the five-lobed liver. This bridge links Galen to almost all of his successors, stressing the impact he had on anatomy despite many of his misconceptions, simply due to the extensive legacy he left behind. Vesalius' work would also have this effect and was to be established as one of the greatest of modern science since Galen.

The Seventeenth Century The seventeenth century led to another progression in the study of anatomy and medicine, where experimental research was carried out as a means of discovering functional anatomy and physiology, insufficiently studied by any the scholars previously mentioned, Galen, Leonardo and Vesalius.

William Harvey, born in 1578, studied at the University of Padua between 1599 and was interested in the study of the movement of blood, inspired by the studies of Aristotle, who maintained that the heart was the origin of the veins and that the organ where all blood converged. Harvey discovered the function of the valves and the direction of flow of venous blood through the simple experiment of pressing and squeezing bulging veins but most importantly applied Galileo's notion of quantitative inquiry in biological experiments to discover the circulation of blood. Harvey solved the problem of haemodynamics by measuring that the volume of blood pumped into the aorta by the heart in half an hour is greater than the total volume of blood in the body. Thus, the blood must be the same which is pumped around the body in a circular motion from the heart, through the aorta and to the whole body.

Although Harvey's discovery was based on mathematical calculations, he sustained the "modern" method of teaching anatomy through dissection and encouraged students to study and uncover anatomy for themselves. (Del Negro, 2003). Conclusion Arguably, human cadaveric dissection and comparative anatomy with dissection of small animals, is at the basis of the majority of anatomical discoveries of the past. I would like to suggest that the fluctuation in popularity throughout the ages of human cadaveric dissection as a tool for the study of anatomy, was due to an innate human fear based on the religious and popular belief which maintained that meddling would lead to the rage of God. This was often justified by proposing that dissection be used solely as a means to illuminate God's perfect creation of the human body. However, I would argue that scholars were aware of the essentiality of dissection for the study of anatomy and after Vesalius, would ascertain that primary human cadaveric dissection rather than animal dissection was able to provide the most accurate and reliable knowledge of human anatomy.

Scholars such as Harvey established their most renowned discoveries utilising not only dissection but human surface anatomy, again emphasising the importance of independent study of anatomy on the human body in order to completely understand the human body. Today, cadaveric dissection is one of the most important tools used at medical schools in order to impart a deeper knowledge of topographic anatomy in the third-dimension.

Arguably, human dissection also teaches respect, empathy and compassion amongst medical students and the process of body donation, currently the only source of bodies for dissection, contributes to the students' understanding of their responsibility within society. The endeavour to a direct approach and central focus of dissection by the scholar as the main medium for the study of anatomy will lead to the advancement of this ever-growing field of medicine.