Notes, iir. 4. 199 



large and unbranching vessel. There are indeed two branches from the great vessel, the 

 one which goes to the lung {Jmlmonary artery), and one which goes to' the backbone and 

 last cervical vertebra {azygos vein). The one which goes to the lung (pulmonary artery"^ 

 divides into two, as the lung itself consists of two parts," and sends branches which 



accompany each air-pipe the branches of the vessel being above the branches 



of the wind-pipe. The vessel which goes to the cervical vertebra and backbone 

 (z*. azygos) runs back along the backbone, and gives off branches to each rib and vertebra, 

 'ultimately dividing into two, opposite the vertebra next above the kidney {thi left and 

 right azygos veins which in man unite somewhat higher up, but also are often united by a 

 cross branch about this point. See Ofay's Anai. f. 241). ' Such are the divisions of these 

 branches of the great vessel. The main trunk of the great vessel, in the part which extends 

 from the heart above these'branches [vena cava superior above point where azygos joins it), 



splits in two directions {vencE innbminata:) Such is the distribution of the vessels 



above the heart. But the part of the great vessel which is below the heart {;vena cava 



.inferior) passes down from above through the diaphragift The branches of the 



smaller vessel which is called tJie aorta are distributed exactly in the same way as those of 

 the great vessel (venous system)^ and its branches accompany those of the latter, being 

 hoWever much smaller, etc." (H.A. iii. 3). 



These passages leave no possible doubt as to what A. meant by his three cavities. If 

 any further prctof were wanting that the largest cavity is not meant to designate the right 

 auricle but the right vefttricle, it is furnished by the following passage: "There are 

 sinews (i.e. chordce tendine^B) inside the largest cavity of the heart"; for there are such 

 in the ventricle, but not in the auricle. 



It is almost superfluous to say that the size of an animal does not in any way determine 

 the number of cavities in its heart. Galen (De JJsu part. vi. 19) points out A.'s mistake, 

 and says that the horse has nomore than the sparrow, the ox than the mouse. It is not 

 impossible that the blunder may have arisen from observation,- though of very imperfect 

 kind. The largest arrtmals knbwn were of course mammals, with four cavities. The huge 

 crocodile, again, has four, while the other and smaller reptiles have but three. Cetacea 

 again, though A. knew them to be really mammals, were classed by the vulgar with 

 fishes, and have four cavities, while the smaller aquatic animals with .which they 

 were usually confounded have two. . • 



24. The passages quoted in the last note show what is meant by the great vessel and 

 the aorta. The former corresponds to the venous system, including the two venje cavse, 

 the right auricle, which was considered to be the dilated junction of these, and the 

 pulmonary artery, which is described as a continuation of the great vessel on the other 

 side of the heart. The aorta and its branches are of course the arterial system. The 

 differences noted by A. between the two are that the arteries have much thicker and 

 firmer, walls than the veins (H. A. iii. 3, 13) ; that the foxmer are of smaller calibre than 

 the latter (ZT. A, iii. 4, i), and as a rule lie in front of them ; and lastly that the two 

 contain different kinds of blood, that in the aorta and the- middle cavity of the heart 

 being purer th^n that in the great vessel and its cavity, the right ventricle. The difference 

 in purity was shown by difference in colour. "Blood is red; but that which is of 

 inferior quality, either naturally or from disease, is of a darker tint" (^H. A. iii. 19, 3). 



25..' Frantzius translates,. "If the blood be of, two kinds and each kind be kept 

 separate,"' and considers the passage of importance as- showing that A. recognized 

 differences between arterial and venous blood. That A. did recognise such differences is 

 certain, but I do not think he alludes to them here.- For Zi(^vi\%.'\s never used- in this 

 treatise to express "zweifacher natur^" but is invariably applied to organs of similar 



