38 HISTORY OF THE HUMAN BODY 



rections and thus gave origin to the Primates, the Condy- 

 larthra, a generalized form of ungulate, and probably a line 

 of aquatic carnivorous forms, destined to become the most 

 erratic and singular of all mammals, the Cetacea, or whales 

 and porpoises. These earliest ancestors of divergent lines 

 were very much alike, and the early primate, carnivorous, 

 and hoofed forms, were all very generalized, and without the 

 differential characteristics that their descendants later de- 

 veloped. The most primitive of the Primates were a group 

 called the Mesodonta, of which the modern lemurs are the 

 most direct descendants. Very early, however, forms like the 

 modern monkeys, Anthropoidea, began to make their appear- 

 ance, forms in which the orbit was entirely separated from 

 the temporal fossa, and in which the dentition was the same 

 as in the monkeys of the Old World and in Man ; and in these 

 we find the direct human ancestors. 



The creodont stem developed, as stated above, the modern 

 Carnivora, including the cats, dogs, bears, and weasels, and 

 from this, at an early date, there probably arose a carnivorous 

 line that adapted itself to the sea. This is the Pinnipedia, or 

 those with fin-like feet, the seals, the walrus, sea-lion, etc. 



The remaining stem, that of the Condylarthra, was per- 

 haps the most prolific of all in respect to the amount of vari- 

 ation, and the extent of modification, for it has produced the 

 Sirenia, aquatic forms, nearly as highly specialized as the 

 whale ; the Proboscidia, or elephants, with an excessive modifi- 

 cation of the nose; and an enormous variety of animals 

 with a reduction of toes, the series reaching its absolute limit 

 in the horse, which has lost all the digits but one, this be- 

 coming greatly strengthened to serve the purpose of an en- 

 tire foot. 



The original Condylarthra have long been extinct, as well 

 as the earlier derivatives, the Amblypoda, Ancylopoda, Taxe- 

 opoda, and Litopterna; but, fortunately, of all these there is 

 left a single solitary Genus, Procavia or Hyrax, for which 

 the Order Hyracoidea has been made. This is a little animal 

 of about the size of a rabbit ; the one referred to in the King 



