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Animal anatomy

The title page of the Fabrica is full of details illustrating one aspect or another of Vesalius’ work. In the lower left we see a boy holding a monkey with a belt around its waist to which a leash is attached. This reminds the viewer that much of Galenic anatomy was based on that of the Barbary Ape because in Galen’s time human dissection was not allowed and the anatomist had to rely on the animal that was closest to the human in most of its features. Vesalius refers scornfully to “Galen and his apes,” and tried whenever possible to show the difference when Galenic anatomy went astray. In the lower right, the title page shows a man holding a dog, which was joined by a sheep the 1555 version. This alludes to the use of common farm animals to supplement hard-to-get human cadavers in anatomical demonstrations. The long-standing reliance on animal specimens had led to misunderstandings such as the belief that human blood was purified by a “marvellous network” or rete mirabile in the neck. Such a plexus is found in sheep and certain other ungulates (where is cools the blood) but not in humans. The young Vesalius had been taught that this was a human feature and believed in its existence early in his career. Ascribed by Galen to “those around Herophilus,” the reticular plexus had become an important fixture of Galenic physiology, supposedly converting vital spirit to animal spirit. Vesalius had depicted this imagined feature of human anatomy in Tabula III of Tabulae anatomicae sex (1538); but on p. 642 of the 1543 Fabrica, he admits “I cannot sufficiently marvel at my own stupidity; I who have so labored in my love for Galen that I have never demonstrated the human head without that of a lamb or ox, to show in the latter what I could not in the former, lest forsooth I should fail to display that universally familiar plexus.” Mundinus (1316) and Massa (1536), meekly following Galen, had affirmed its existence in humans; only Berengario da Carpi expressed his scepticism. Jacob Sylvius’ In Hippocratis et Galeni physiologiae anatomicam isagoge, written about the same time as Vesalius’ Fabrica, acknowledged its absence in humans but implied that human anatomy had changed since Galen: it “still appears today in brutes.” The reluctance of Renaissance authorities to challenge Galen openly concerning this feature testifies to his enduring authority.

Though he was quick to criticize Galen for confusing animal and human anatomy, Vesalius’ illustrations often include animal specimens and animal features. His illustration of a human skull resting on that of a dog appears twice in the Fabrica. Its purpose was to show that certain foramina described by Galen occur only in the canine skull. But other canine features shown in the Fabrica are not acknowledged: The left hyoid bone shown in Bk I Ch.13, fig. has a canine feature in the chain of narrow ossicles (shown here in color) that extend in the dog to the styloid bone (in the human, this connection is made by the stylohyoid ligament). The epiglottic cartilage in the larynx (Bk. I Ch. 38, figs.12–13) is similarly canine in its general aspect. Sometimes Vesalius acknowledged the substitution of animal for human anatomy. Baldasar Heseler reported that Vesalius used “the larynx of an ox and of some other animals” in a 1540 anatomy lecture at Bologna “because, he said, in the hanged [human] subjects we cannot see the larynxes, for they are destroyed by the noose, but they are however quite different [in man and in animals].” (Eriksson 1959, 285). Vesalius’ illustration of the tongue in Book II Chapter 19 is too long to be human — though here Vesalius says nothing: its comparative length suggests it is from a dog, cow, pig, sheep, or similar quadruped. When demonstrating the eye in lectures, anatomists commonly substituted the much larger eye of an ox because it was easier to see in a large room. Vesalius’ seventh muscle [m. retractor bulbi] of the eye (shown here in yellow) is found in a number of ruminants but not in thehuman. The eye illustrated is probably that of a domesticcow or ox, since its structures are easier to observe.This is another case where Vesalius’reliance on Galenic authority has taken precedence over direct observation — though he is rightly skeptical of the use attributed to this muscle. In De anatomicis administrationibus Galen had recommended that students dissect the eye of larger animals (where this muscle would be present) rather than that of the ape. The historiated capital R in the 1543 edition shows the eye being removed from the head of a cow.

At least once in the Fabrica, Vesalius deliberately combined human and animal anatomy in a single specimen to show an error in Galen. In baboons and dogs, the rectus abdominis extends farther toward the neck than in humans and had been describederroneoudly (for humans) by Galen. To illustrate the error, Vesalius showed the animal muscle on a human in his fifth “muscle man” in Book II, where r to t (marked here in color) illustrates theextended portion of the m. rectus abdominis in the dog and baboon, not found in humans. Vesalius added this explanation in his 1555 edition: “The wide tendon and this fleshy part are the muscle that Galen counts the fifth of those moving the thorax, but it is not to be seen in humans as it is in caudate apes and dogs. We have nevertheless drawn it here so that Galen can be understood.”

Comparative anatomy in antiquity and the early modern period was the source of some confusion. Though Vesalius hoped to resolve some of the errors in human anatomy that resulted, the Fabrica was not altogether free of such errors.