4^4 ROSS ON EVOLUTION. 



characteristic of the Orders of Animals, which preserve the power 

 of free motion, and which progresses in each in time from the 

 earliest j^eriod in which we can trace it as a distinct Order, by- 

 means of its fossil remains, to the present day. This is manifested 

 by the increasing comparative size of the brain cavity, the lessening 

 and sometimes complete atrophy of the posterior extremity or tail, 

 also by the concentration of the limbs around the anterior extremity 

 and their adaptability to serve its purposes. A shortening of the 

 jaws and increase of the facial angle is also usually characteristic of 

 progress in time among higher Orders of Animals ; and in Man, as 

 is well known, it is one of the most obvious distinctions of the 

 higher Races. 



In Man the process of cephalization has its fullest realization. 

 The facial angle, that is, the angle made by a line passing from the 

 forehead over the upper jaw, meeting another line passing along 

 the base of the skull, is in the best developed specimens, nearly a 

 right angle. It is true that in the lower Races it is considerably 

 less than this. In the most anthropoid of the Apes it is still less, 

 and it is remarkable that it is less in these when mature than when 

 young, shewing that they in common however, as has been already 

 shewn, with all Vertebrates lower than Man diiferentiate from 

 homoiogical symmetry as they approach maturity. Next to these 

 come successively other groups of Monkeys of the great Continent, 

 all of which have the same number of teeth as Man, and compara- 

 tively narrow noses, hence called Catarrhines, while the Monkeys 

 of America, except a peculiar group, have one tooth more, a 

 grinder, on each side above and below, longer jaws and broader 

 noses, hence called Platyrhines. In Man only is the attitude 

 entirely erect, the fore limbs being thoroughly adapted for use as 

 prehensile organs, — instruments of wonderful adaptability as minis- 

 ters to his will. In these respects there is a corresponding gradation 

 among the monkeys, the Oatarrhines having the thumb opposable 

 to the fingers, and the hand generally rather adapted for use as a 

 hand than a foot, and many species are like man without a caudal 

 appendage, while the Platyrhines have not the thumb opposable, 

 but have long prehensile tails. Other groups of Monkeys are still 

 more differentiated, aiid have been described as Squirrel-like or as 



