. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. BRAIN 215 \ is relatively much smaller than in Elasmobranchs and Teleosts: it gives rise to a valvula cerebelli, and a complicated choroid plexus roofs over the fourth ventricle. Amphibians.—The cerebral hemispheres of the Amphibia are distinguished from those of the Dipnoi by a higher development of the pallium, which, however, is differentiated even in the latter group into an external layer of nerve fibres and an internal cellular layer (central gray matter). The basal ganglia (corpora striata) are less marked, except
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. BRAIN 215 \ is relatively much smaller than in Elasmobranchs and Teleosts: it gives rise to a valvula cerebelli, and a complicated choroid plexus roofs over the fourth ventricle. Amphibians.—The cerebral hemispheres of the Amphibia are distinguished from those of the Dipnoi by a higher development of the pallium, which, however, is differentiated even in the latter group into an external layer of nerve fibres and an internal cellular layer (central gray matter). The basal ganglia (corpora striata) are less marked, except in the Gymnophiona, and merely form a more or less prominent thickening of the wall of each hemisphere projecting into the lateral ventricle. A hippocampal lobe is not distinctly developed, but a hippocampus is represented by elevations of the central gray matter, which are con- nected right and left by a small anterior pallial commissure just above the anterior commissure (Fig. 164, ]>) The Amphibian brain docs not, how- ever, lead directly towards that of Reptiles. Although the telencephalon is more highly differentiated than in lower forms, the cli- encephalon and mesencephalon are sim- pler than in Fishes; and, on the whole, the brain of Amphibians is less com- plicated than that of any other Verte- brates, except Lampreys. In Urodeles the individual parts are more elongated and separated from one another than in Anurans, and the dien- cephalon is therefore more freely exposed. The hemispheres are almost cylindrical, and the olfactory lobes are distinct from one another, while in the Anura they are fused for a short distance anteriorly (Fig. 164). The diencephalon and optic lobes are much broader in Anurans than Urodeles. The cerebellum consists. - Fid. 163.—BKAIN OF Cera- tod'iis foxteri. Dorsal view. (From Parker and Haswell's Zoology.) and, auditory nerve ; chl, cerebellum ; fac, facial nerve ; ijf, glossopharyn- geal; med, medulla ob- longata; mes, mesen- ce
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