392 THE SENSORIAL FUNCTIONS. 



« 



Trigla lyra, or Piper Gurnard, (Fig. 451,) and in the Mu- 

 rxna conger, or Conger Eel, (Fig. 452,) are scarcely dis- 

 cernible. They are very small in the Percct Jluviatilis, or 

 common Perch (Fig. 453;) but more developed in Reptiles, 

 as in the Tcstudo inydas, or Green Turtle, (Fig. 454,) and in 

 the Crocodile, (Fig. 455;) and still more so in Birds, as is 

 seen in the brain of the Dove, (Fig. 449;) but, most of all, 

 in the JNIammalia, as is exemplified in the brain of the Lion, 

 (Fig. 456.) On the other hand, the optic tubercles (t) are 

 largest, compared with the rest of the brain, in Fishes; and 

 their relative size diminishes as we ascend to Mammalia: 

 and the same observation applies also to the olfactory 

 lobes, (o.) 



The relative positions of the parts of the brain are much 

 influenced by their proportional development. This will be 

 rendered manifest by the lateral views of the brains of the 

 Perch, the Turtle, the Dove, and the Lion, presented in 

 Figures 457, 458, 459, and 460, respectively, where the 

 same letters are employed to designate the same parts as in 

 the preceding figures. In Fishes, all the tubercles which 

 compose this organ, are disposed nearly in a straight line, 

 continuous with the spinal marrow, of which, as they scarce- 

 ly exceed it in diameter, they appear to be mere enlarge- 

 ments. As the skull expands more considerably than the 

 brain, this organ does not fill its cavity, but leaves a large 

 space filled with fluid. Some degree of shortening, how- 

 ever, may be perceived in the brain of the Perch (Fig. 457;) 

 for the medulla oblongata (m) is doubled underneath the ce- 

 rebellum (c,) pushing it upwards, and rendering it more 

 prominent than the other tubercles. This folding inwards, 

 and shortening of the whole mass, proceeds to a greater extent 

 as we trace the structure upwards, as may be seen in the brain 

 of tlie Green Turtle (Fig. 458.) In that of Birds, of which 

 Fig. 459 presents a vertical section, the optic tubercles have 

 descended from their former place, and assumed a lateral po- 

 sition, near the lower surface of the brain, lying on each side 

 of the medulla oblongata, at the part indicated by the letter 



