. The chordates. Chordata. tchthyopsida 119 than the vertebrate nervous system. The brain of the iish is differenti- ated into five regions which, beyond question, correspond structurally and, at least in a general way, functionally, to the five main divisions of the human brain (Fig. 324). In the telencephalon, however, cerebral hemispheres are poorly developed, and their roof, the pallium, con- tains little or, in most fishes, no nervous tissue. In modern fishes, there are 10 pairs of cranial nerves. The autonomic nervous system is well developed. The "five senses" of man (but in r
. The chordates. Chordata. tchthyopsida 119 than the vertebrate nervous system. The brain of the iish is differenti- ated into five regions which, beyond question, correspond structurally and, at least in a general way, functionally, to the five main divisions of the human brain (Fig. 324). In the telencephalon, however, cerebral hemispheres are poorly developed, and their roof, the pallium, con- tains little or, in most fishes, no nervous tissue. In modern fishes, there are 10 pairs of cranial nerves. The autonomic nervous system is well developed. The "five senses" of man (but in reality he has several more than five) are provided for in fishes by organs which differ only in details and in degree of efficiency from corresponding organs in mammals. Eyes, ears, and olfactory (nasal) organs are well developed in fishes. In the mouth are organs of taste, but—unlike anything found in Amniota—sense-organs similar to the oral organs of taste commonly occur on the external skin, especially on the head and sometimes far back on the trunk and even on the fins (see p. 196). Apparently many fishes may become aware of the proximity of food by "tasting" it through the skin. The skin is also well supplied with tactile sensory structures but in a limited variety of types as compared to the skin of land animals. In addition to these external organs of chemical and tactile sense, fishes have an integumentary sensory equipment which has no exact. Fig. 324. Sagittal section of brain of trout, (aq) Aqueduct; (bo) bulbus olfac- torius; (ca, ch, ci, cp) anterior, horizontal, inferior, and posterior commissures; (cc) central canal; (cl) cerebellum; (cs) corpus striatum; (h) hypophysis; (i) infundib- ulum; (li) inferior lobe; (oc) optic chiasma; (p) pallium; (pi) pinealis; (sv) saccus vasculosus; (//) torus longitudinalis; (to) tectum of optic lobes; (v) velum trans- versum; (v3, vA) ventricles; (vc) valvula cerebelli; (I) olfactory nerve; (IV) trochlear nerve. (Af
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