DOG-FISH. , II 



NERVOUS SYSTEM. 



Fishes inhabit water in every part of the globe, and occupy it. 

 at different depths, and are required to subsist on various sorts; 

 of nourishment ; and as they must therefore have different 

 capacities, they must have corresponding variations in the- 

 structure of their bodies. The appetite for food appears to" be 

 their predominant desire, and providing for its gratification to 

 form their chief occupation : and as this is very voracious, they 

 must be constituted not only with a peculiar digestive apparatus, 

 but with subtlety for taking their prey, and strength for pursu- 

 ing it, as well as for defending themselves against the attacks of 

 their enemies. To the varying functions of the different organs', 

 the nervous system is appropriately adapted. When the sense of 

 smelling is most conducive to their convenience, as in the dog- 

 fish, there is a capacious nose, large olfactory nerves, and large- 

 anterior lobes of the brain ; and when seeing is more advantageous, 

 as in the cod, the anterior lobes are smaller, and the olfactory 

 nerves decrease in the same ratio ; the eyes are consequently 

 large, and the optic nerves and parts of the brain from which 

 they originate are proportionate with them. Besides the different. 

 form and size of the several portions of the brain generally 

 existing, it is furnished with additional lobes when extraordinary 

 powers are necessary. 



Brain consists of a large cerebellum covering the fourth ven- 

 tricle, the sides of which are folded, and known as the restiform- 

 bodies. In front of the cerebellum is the mesencephalon, and in. 

 front of this the thalamencephalon. The cerebral hemispheres 

 are united in the middle line ; the olfactory lobes are cpntinued 

 from the anterior lateral portion of the cerebrum, and they dilate- 

 into large ganglionic masses before they enter the olfactory 

 sacs. 



The optic nerve is seen passing to the eye. The third nerve 

 is seen passing to all the muscles of the eye, except the superior 

 oblique and external rectus. The fourth is seen passing tp the 

 superior oblique muscle, and the sixth to the external rectus. 

 The fifth is seen giving off three principal trunks beside the 

 auditory. The first passes in. two divisions through the orbit ; 

 these become united at the anterior part of this cavity, and the 

 nerve is then continued forwards, giving branches to the cellular 

 structure in its course towards the end of the snout. The second 

 trunk passes on the fore part of the muscles of the jaw, gives a 

 large branch, which distributes filaments to these muscles and the 

 upper and lower lips; it gives a large branch to the cellular 

 structure on the ventral surface of the snout, this also gives, 

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