THE ORIGIN OF MAN 117 



equal simplicity, that primitive conditions are more widely 

 departed from in the monkeys, and are finally lost by new 

 adaptations in such specialised quadrupeds as the Ungulates. 

 Far from the human condition being the last perfected 

 specialisation it is, in these cases, the most primitive and least 

 specialised type, from which the other forms have diverged 

 in different directions. 



In the vascular system the same story is unfolded. The 

 arrangement of the vessels of the aortic arch in Man is exactly 

 the same as that in Ornithorhynchus, and for many reasons 

 it must be regarded as singularly primitive. The anthropoid 

 apes at times retain this primitive form, but at others they 

 are modified in the manner of the monkeys a modification 

 which is carried to greater lengths in the typical specialised 

 quadrupeds. In those instances in which the peripheral 

 vessels of the other Primates differ markedly from the typical 

 human plan it will be foiind that the human form is the least 

 specialised. This applies to such characteristically simian 

 vessels as the arteria saphaena, which is certainly not a primi- 

 tive blood-vessel of the leg. 



Despite the wonderful role it performs in the function of 

 speech, the human tongue is in structure a remarkably primi- 

 tive organ, which differs widely from that which is typical 

 of the monkeys. The tongue of the chimpanzee approaches 

 very near to the human type, and were it not that the tongues 

 of undoubtedly primitive mammals are ready for comparison, 

 it would be easy to assume that the tongues of the chimpanzee 

 and Man were specialisations of the condition seen in lower 

 monkeys ; when as a matter of fact the very reverse is actually 

 true. The case of the tongue is particularly instructive in the 

 study of the origin of minor anatomical details, since the two 

 small sublingual folds (plica fimbriata and plica sublingualis), 

 which are relatively extremely well developed in Man and the 

 chimpanzee, are singularly like the same structures in certain 

 lowly mammals. But while the American monkeys depart 

 from such a condition in one direction, by the retention of 

 the plica fimbriata, the Old World monkeys are specialised in 

 the other, by the retention of the plica sublingualis. The 



