.'. Notes, iii. 4. . 197 



scheme, the main instruments of motion. Of the contractility of muscular tissue he knew 

 nothing ; though it is impossible to suppose that he did not know that what we call 

 a muscle swelled up, becoming shorter and broader, during action. The changes of 

 shape for instance in the Biceps, perfectly well known to every painter and sculptor, 

 cannot possibly have escaped his notice. Such a muscle however he considered to have 

 two constituents ; firstly flesh, that is the true red muscular tissue, which' he supposed 

 to be nothing more than an aggregate of small vessels clogged up with inspissated blood 

 (iii. 5, Note 7) ; and, secondly, tendinous fibres and other fibrous elements such as the 

 muscular sheath, etc., which he supposed to be the ultimate " terminations of the arteries, 

 converted into solid strings. The action of the muscle he attributed not to the former of 

 these elements, the red muscular tissue, but to the latter, the really inactive tendinous 

 fibres, which have, he says, a transverse extensibility, that is to say can become broader 

 and shorter. 



His idea of the" mode in which these tendinous parts were called into play seems to 

 have been as follows. The heart, as it is the centre of the nutritive 'and the sensory 

 principles, ^ so also is the centre of voluntary motion. By its independent (cf. ii. 16, 

 Note 11) contractions and relaxations (for it is as it were a distinct living being within 

 its possessor) it acts upon the chordae tendinese, and either directly or through these upon 

 the fibrous aorta. This in turn acts upon- the tendinous fibres of the muscles, which 

 are in fact its terminal branches, and these fibres become transversely extended, and 

 consequently longitudinally shortened ; these again act in turn upon the true tendons 

 and ligaments, by which the bones are set in motion. 



The want of continuity in the tendinous system of which A. speaks is the gap between 

 the chordae tendinese and the true tendons attached to tlie bones, a gap which he fills up 

 by the tendinous aorta and its branches. 



Such I take to be A.'s inadequate conception of the mechanism of motion. That he 

 himself felt how unsatisfactory it was, we may infer from his saying so vary little on 

 the subject, notwithstanding its importance. We must remember, moreover, that, while 

 nerves were still undiscovered, no explanation of voluntary motion was possible. A. had 

 to find some anatomical machinery connecting the tendons, which were clearly the 

 immediate agents that acted on the bones, with the volitional centre, which he took as 

 we know to be the heart and not the brain. He could find no other continuous substance 

 between these two, than somri or other kind of fibrous tissue, in the form either of 

 tendinous fibre or of arterial wall. This therefore he assumed to be Ihe intermediate 

 agent, no other being apparently forthcoming. 



1\. This is one of many passages showing that A. himself practised dissection. 

 .22. .Cf. H. A. ii. 15, 6. It is "not uncommon to find in large mammalia, especially, in 

 Pachyderms and Ruminants, a cruciform ossificarion in the heart, below the origin of the 

 aorta. In • the ox this is a normal formation, as also in the stag. But in Pachyderms, 

 or at any rate in the horse, it is only found in old individuals, and appears to be the 

 result of pathological degeneration. Galen, in his manual of dissections, tells a curious 

 story * of the triumph • he obtained over the assembled physicians of Rome by his 

 demonstrating the presence of a bone in the heart of an elephant when they had failed to 

 find it. See also De Usu part. vi. 19. • 



23. A full description of the heart is given in the Hist. An. (i. 17, and iii. 3). . There, 

 as here, it is stated that it Jias only three cavities. Aubert and Wimmer (i. 238) suppose 

 that A., took the two auricles to form one cavity, viz. that which he terms, the right 

 cavity. Frantiius supposes that the left auricle was overlooked. Both commentators 

 thus make the- second and third of A.'s cavities correspond to the right ajid left ventricles 



