In less than fifty pages Vesalius describes the contents of the thorax.
He writes intelligently of the membrane lining the thorax, and then
gives an account of the arteria aspera, as the trachea was formerly
named. Passing on to the lungs, he next takes up the anatomy of the
heart. He describes its position, form, and structure in better terms
than had been done by preceding anatomists. The auricles, ventricles,
and valves are carefully examined. His illustrations of both lungs and
heart are excellent.
In the 1543 edition of the _Fabrica_, Vesalius adopts the erroneous view
of Galen that openings exist in the septum of the heart. In the second
edition of his book, published in 1555, he says that influenced by the
views of Galen, he believed that the blood passes from the right to the
left ventricle of the heart, through the septum, by means of the pores.
Vesalius immediately adds that the septum of the heart is as dense and
compact as the rest of this organ, and that not the smallest quantity of
blood passes through the septum.
His account of this subject is best given in his own words:—“In
recounting as above the structure of the heart, and the use of its
different parts, I have followed in the main the doctrines of Galen; not
that I regard them in all particulars as consonant with the truth, but
because, in attributing new functions and uses to a number of parts, I
am still distrustful of myself, and not long ago should hardly have
ventured to differ from that Prince of Physicians by so much as a
finger’s breadth. As for the dividing wall, or septum, between the
ventricles forming the right side of the left cavity, the student of
anatomy should consider carefully that it is equally thick, compact, and
dense, with all the rest of the cardiac substance enclosing the left
ventricle. And accordingly, notwithstanding what I have said about the
pits in this situation, and at the same time not forgetting the
absorption by the portal vein from the stomach and intestines, I still
do not see how even the smallest quantity of blood can be transfused,
through the substance of the septum, from the right ventricle to the
left”.
Vesalius and other anatomists knew of the hepatic circulation, or at
least believed in some communication between the portal and hepatic
veins:—“The branches of this vein”—vena cava—“distributed through the
body of the liver, come in contact with those of the portal vein; and
the extreme ramifications of these veins inosculate with each other, and
in many places appear to unite and be continuous”.
Vesalius knew that in several particulars the accepted physiology of the
vascular system was wrong. If he could have lived a few years longer, it
is possible that he might have solved the great problem which was made
clear by William Harvey. In the light of our present knowledge some of
Vesalius’s words are suggestive:
“When these matters are taken into account, many things at once present
themselves in regard to the arterial system, which deserve careful
consideration; especially the fact that there is hardly a single vein
going to the stomach, the intestines, or even the spleen, without its
accompanying artery, and that nearly every member of the portal system
has a companion artery associated with it in its course. Again, the
arteries going to the kidneys are of such size that they can by no means
be affirmed to serve merely for regulating the heat of these organs; and
still less can we assert that so many arteries are distributed to the
stomach, intestines and spleen for that purpose alone. And there is,
furthermore, the fact, which we must for many reasons admit, that there
is through the arteries and veins a mutual flux and reflux of materials,
and that within these vessels the weight and gravitation of their
contents has no effect”.
The Seventh Book.
In the seventh book, consisting of less than sixty pages, Vesalius fully
describes the anatomy of the brain, of the cranial nerves, and of the
organs of sense. His description of the eye is not as near accuracy as
might be expected. He places the crystalline lens in the centre of the
globe. His description of the organ of vision was only slightly better
than that which was given by Galen. Vesalius showed, however, that the
optic nerve is not a hollow tube, and that it does not enter the eyeball
exactly in the antero-posterior axis.