25 



abstruse or controverted questions ; — such, for instance, as 

 the attempts that have been made to homologize the 

 nervous system of Articulates with that of Vertebrates, upon 

 which he has some acute criticism; — the theories that 

 have been propounded respecting the functions of the cere- 

 bellum and its relation to locomotion, which he tests in a 

 characteristic way by a direct appeal to facts ; — the supposi- 

 tion of Cuvier that the special enlargements of the spinal 

 cord are in proportion to the force of the respective limbs 

 supplied therefrom; which he controverts decisively by 

 similar appeal, an extract from which I beg leave to append 

 in a note. 1 



So, in describing the structure of the optic nerves in the 

 frog, and the development of the eye and optic lobes, he pro- 

 ceeds to remark, that — 



" The instances of Proteus and Amblyopsis naturally sug- 

 gest the questions, whether one and the same part may not 

 combine functions wholly different in different animals, and 



1 "If by force is meant the muscular energy and development of the limbs, this 

 statement does not appear to be sustained in the present instance, nor in many 

 other instances brought to notice by comparative anatomy. In man the brachial 

 enlargement is always larger than the crural, though the legs are so much more 

 powerfully developed than the arms, and the same is true of the greater number 

 of mammals. In frogs there is a still greater disproportion between legs and arms 

 yet there is not a corresponding difference in the size of the bulgings. They can- 

 not, therefore, be said to be in proportion to the muscular force only of the limbs, 

 but correspond far more nearly to the acuteness of the sense of touch, which in 

 man and mammals is more delicate in the hands and arms than in the legs and 

 feet. In bats, it is true that the muscular force of the arms is greater than that of 

 the legs, and that the brachial far surpasses the crural enlargement; but, at the 

 same time, the sense of touch in the membranes of the wings is exalted to a most 

 extraordinary degree. In birds the posterior bulging is almost universally the 

 largest, though this condition is in part dependent upon the presence of the rhom- 

 boidal sinus. In these animals, while the muscular energy of the wings is the 

 most developed, the sensibility of the feet is the more acute." 



