io8 THE HUMAN SPECIES 



but in the double-breathing animals, a muscular partition 

 divides the auricle into two parts, a right and a left auricle. In 

 the reptiles we find not only the auricle but also the ventricle 

 thus divided, and in the crocodile the two parts are quite 

 separate. In birds the division, both in the heart and in the 

 larger arteries, is so complete that arterial blood nowhere 

 mingles with venous blood. The auricles of the mammals 

 have been formed through retrograde development of the 

 anterior auricular division, and in the interior of the heart, in 

 the higher mammals, the muscular trabeculae lie closer to the 

 wall of the chamber and there form the so-called papillary 

 muscles with their tendinous endings attached to the mem- 

 branous valves. In reptiles and birds, the aortic arch is on the 

 right, but in all mammals and in man, on the left. The carotis 

 interna is more important than the externa, the latter taking 

 the form of a mere branch of the carotid artery, mainly for 

 carrying on the work of circulation in the tongue and the region 

 of the lower jaw. In man and the apes the vessel called the 

 carotis externa may be said to form a trunk with numerous 

 branches proceeding from the carotis communis. 



The distribution of the upper arteries differs, in some 

 respects, in man and certain of the apes and semi-apes, and, 

 in other respects again, there is a distinction between man and 

 certain other of the apes and semi-apes. A truncus brachio- 

 cephalicus dexter, a carotis sinistra and subclavia sinistra are 

 special characteristics of man, the anthropoids, a few Prosimiae 

 (e.g., Aye-aye), the seal, many rodents, certain of the edentata 

 (Bradypus and Dasypus), the hedgehog, some of the marsupials 

 (Phascolomys) and the monotremata. On the other hand, a 

 truncus brachiocephalicus dexter and a subclavia sinistra with 

 separate origin of the two carotids from the truncus brachio- 

 cephalicus is present in certain apes, (e.g., Macacus) and in many 

 of the prosimise (Loris, Galago), as also in many of the carni- 

 vora and rodents, in pig, pangolins and muskdeer. 1 The arteria 

 saphena which man originally possessed has disappeared during 

 the course of his history owing to the erect position and the 

 consequent expansion of the vessels (Popowsky), and has been 

 replaced by the larger arteria peronea and arteria glutaea 



1 C. Gegenbauer, Vergl. Anat., 2nd edition, 1870, p. 843. 



