. Animal physiology. Physiology, Comparative; Physiology, Comparative. NERVOUS SYSTEM OF FISHES AND REPTILES. 347. Fjg. 181.—Brains of Fishes. A, Cod ; B, Shark. considerably in different fishes; thus in the Cod, they are much smaller than those which suc- ceed them ; whilst in the Shark they are as much larger. These are the cerebral hemispheres (ch). Behind these, again, are two large masses, op, the optic gan- glia, in which the optic nerves terminate. And at the back of these, overlying the top of the Spinal Cord, is a single mass, the cerebellum (ce) ; this is seen to be much larger in th
. Animal physiology. Physiology, Comparative; Physiology, Comparative. NERVOUS SYSTEM OF FISHES AND REPTILES. 347. Fjg. 181.—Brains of Fishes. A, Cod ; B, Shark. considerably in different fishes; thus in the Cod, they are much smaller than those which suc- ceed them ; whilst in the Shark they are as much larger. These are the cerebral hemispheres (ch). Behind these, again, are two large masses, op, the optic gan- glia, in which the optic nerves terminate. And at the back of these, overlying the top of the Spinal Cord, is a single mass, the cerebellum (ce) ; this is seen to be much larger in the active rapacious Shark, the variety of whose movements is very great, than in the less energetic Cod. The Spinal Cord (sp) is seen to be divided at the top by a fissure, which is most wide and deep beneath the cerebellum, where there is a complete opening be- tween its two halves. This opening corresponds to that through which the oesophagus passes in the Invertebrata; but, as the whole nervous mass of Yertebrated animals is above the alimen- tary canal (§. 66), it does not serve the same purpose in them ; and in the higher classes, the fissure is almost entirely closed, by the union of the two halves on the central line. 454. In Reptiles, we do not observe any considerable advance in the character of the brain, beyond that of Fishes; save that the Cerebral hemispheres are usually larger, extending forwards so as to cover in the Olfactive ganglia (Fig. 182). The Cerebellum is generally smaller, as we should expect from the inertness of these animals, and the want of variety Fig. 182.—brain in their movements (§. 480). The Spinal Cord is a,°cerebrai bemi- stu"l very large, in proportion to the nervous masses spheres; 6,optic contained in the skull: and, as we shall hereafter ganglia; c, cere- i 7 beiium; a, spinal see, its power of keeping up the movements of the body, after it has been cut off from connection with the brain, is very Please note that
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