498 THE SENSORIAL FUNCTIONS. 



Gurnard), and the Trigla gurnardus (the Grey 

 Gurnard), there are, at the commencement of the 

 spinal cord, numerous enlargements, presenting a 

 double row of tubercles (as seen in the space 

 between m and s. Fig. 451). The nerves from 

 these tubercles supply the detached rays, or feelers, 

 anterior to the pectoral tin.* Fishes M'hich possess 

 electrical organs have a considerable dilatation of 

 the spinal cord, answering to the large nerves which 

 are distributed to those organs. Birds which fly 

 but imperfectly, as the Gallinaceous tribe and the 

 Scatisores, have the posterior enlargement much 

 greater than the anterior ; a disproportion which is 

 particularly remarkable in the Ostrich. On the 

 contrary, the anterior enlargement is much more 

 considerable than the posterior in birds which have 

 great power of flight. In the Dove, of which the 

 brain and whole extent of the spinal cord are shown 

 in Fig. 449, the enlargements (w and l) corre- 

 sponding to the wings and legs respectively, are 

 nearly of equal size. In Quadrupeds, we likewise 

 find the relative size of these enlargements corre- 

 sponding to that of fore and hind extremities. 

 When the latter are absent, as in the Cetacea, the 

 posterior dilatation does not exist. 



The brain (b) has been regarded as an expansion 

 of the anterior or upper end of the spinal cord ; 

 and its magnitude, as well as the relative size of its 

 several parts, vary much in the diff'erent classes 

 and families of vertebrated animals. This will 

 appear from the inspection of the figures I have 



* The relation of these tubercles to the powers of sensation, rather 

 than to those of motion, is apparent from their absence in the true 

 Flying-fish, or Exocoetus voUtans. 



