Page:The Harveian oration 1896.djvu/38

34 HARVEY AND GALEN ventricle of the heart always wanting in animals which had no lungs and did not breathe air, like fishes (but not in all aquatic animals), and concluded that the right ventricle was made for the sake of the lungs h

thought Aristotle might have been misled in the same way.

The views of later commentators are discussed by Dr. William Ogle in his translation of Aristotle On the Parts of Animals (Notes, p. 197).

Some have supposed that the left auricle was not regarded, being empty and inconspicuous after death (an explanation, I think, adopted by Professor Huxley'. Dr. Ogle thinks the three cavities were the right ventricle, the left ventricle, and the left auricle ; and has minutely ex- plained how this is possible. The great difficulty is that Aristotle makes all the cavities communicate with the lung, and does not speak of their communicating with each other. The left ventricle, on its aortic side, can only be regarded as communicating with the lung if the ductus arteriosus of the foetus be re- garded as pervious, and this applies to Vesalius’s explanation as well as Dr. Ogle’s. The question is ex- tremely obscure and perhaps cannot be explained. I confess I lean to the older explanation that Aristotle sup- posed the left ventricle to be divided ; since I cannot believe that he used the word ‘ cavity ’ (xoiia) in a dif- ferent sense to that of all other ancient writers, or that he could have been so completely misunder- stood by his followers as well as by his opponents, all of whom took that word to mean ventricles only. Aristotle was never blamed or ex- cused for saying that the heart con- tained less than four cavities, but only for saying that it had more than two. His supposition that large animals had more cavities of

the heart than small animals is still more difficult to understand.

1 Harvey maintains (MS. Prae- lectiones, fol. 74) that Galen was wrong on this point, and that fishes, having no lungs, want the left ven- tricle, not the right ; that is, their single ventricle represents the right one of higher animals. (In the De Motu Cordis he speaks of the same subject, but his meaning is not so clear.) To ascertain the teaching of modern anatomists and zoologists on this point, I applied to my friend, Professor Ray Lankester, who has favoured me with the following note : — ‘As to the ventricle of Fishes, both Galen and Harvey are wrong. There is a third view, which is cor- rect, viz. that the fish’s ventricle represents both the right and the left ventricles. It becomes divided [in higher animals] by a septum which can be seen gradually becom- ing perfect. The septum first of all divides the great arterial trunk into two passages (functional in the Frog), then grows into or rather from the wall of the ventricle. In most Reptiles it is incomplete, but in Crocodiles is fully formed, so that the ventricle is strictly divided into two. The two auricles, on the other hand, are of independent origin, not formed by division of the original one. That remains as the systemic right auricle. The pulmonary is a new thing, developed on the pul- monary vein.’

Both Galen and Harvey were wrong ! — but both were partially right : an excellent illustration of the two sides of the shield.