Monograph of the Genus Semnopithecus. 321 



setting aside the total absence of a tail. On this point we 

 need not insist. 



If we examine with attention the hands and feet of the 

 Semnopitheci, we shall find the metacarpal and metatarsal 

 bones, and also the phalanges of the fingers greatly elongat- 

 ed, while the thumb, both of the hands and feet, is dispro- 

 portionately small. The thumb of the hands indeed is so in- 

 significant, that it appears almost useless, and can scarcely 

 be regarded as antagonizing with the fingers, or as assisting 

 in the action of grasping. The condition of the thumb is a 

 more important character than might at first be supposed, as 

 will easily be understood when we investigate its develope- 

 ment in other groups of the present family. 



Turning from India to Western Africa, we are presented 

 with a genus, in which the thumb of the fore hands is reduced 

 to so low a degree in the scale, that indeed it cannot be said 

 to exist ; its situation being indicated nearly by a small nail-less 

 tubercle. The genus to which we allude is that of Colobus, 

 which, in fact, may be described as being a repetition of the 

 form of Semnopithecus. In both we have the same small 

 round head and short flat face, the same attenuated contour 

 of body, long slender limbs, and elongated tail, and the same 

 dental formula. Even in the character of the fur, which in 

 many of the Semnopitheci is full, soft, and long, we perceive 

 the accordance. So far then are there two genera intimately 

 related, and if, in Colobus, the thumb of the fore hands be 

 wanting, it is but little more than rudimentary in Semnopi- 

 thecus. By way of note we may here observe that the ab- 

 sence of a thumb is not peculiar to the genus Colobus ; the 

 American genus Ateles, containing the long, slender, prehen- 

 sile-tailed spider-monkeys, is similarly conditioned. It would 

 seem indeed to be a rule, (we here refer more exclusively to 

 the Simiadce), that whenever the limbs and hands are peculi- 

 arly elongated, that such developement takes place at the 

 expense of one of the parts entering into their structure ; in- 

 dependently of the instances already adduced, in which a re- 

 duction of the thumb, even to the minutest rudiment, is ac- 

 companied by such a conformation, we may turn to the orang, 

 in whose structure a similar feature is presented, viz. a reduc- 

 tion of the thumb, in connection with hands and arms of pro- 

 digious elongation. As however we wish to be cautious in 

 promulgating theories, which are often more plausible than 

 true, we shall not push this subject "ad extremum ; " it suf- 

 fices to have hinted at it. 



It is then, we conceive, by means of Semnopithecus on the 

 one hand, and Colobus on the other, that we are furnished 



