[Illustration: From _Cat. R.C.S. England_.
FIG. 17.--Section of the Brain of Porbeagle Shark (_Lamna_).]
In the Amphibia the brain is of a low type, the most marked advances on that of the fish being that the anterior commissure is divided into a dorsal and ventral part, of which the ventral is the true anterior commissure of higher vertebrates, while the dorsal is a hippocampal commissure and coincides in its appearance with the presence of a small mass of cells in the outer layer of the median wall of the pallium, which is probably the first indication of a hippocampal cortex or cortex of any kind (Osborn, _Journ. Morph._ vol. ii., 1889, p. 51).
[Illustration: From _Cat. R.C.S. England_.
Fig. 18.--Section of Brain of Turtle (_Chelone_).]
In the Reptilia the medulla has a marked flexure with a ventral convexity, and an undoubted cerebral cortex for the first time makes its appearance. The mesial wall of the cerebral hemisphere is divided into a large dorsal hippocampal area (fig. 18, _Hip._) and a smaller ventral olfactory tubercle. Between these two a narrow area of ganglionic matter runs forward from the side of the _lamina terminalis_ and is known as the paraterminal or precommissural area (Elliot Smith, _Journ. Anat. and Phys._ vol. xxxii. p. 411). To the upper lateral part of the hemisphere Elliot Smith has given the name of _neopallium_, while the lower lateral part, imperfectly separated from it, is called the _pyriform lobe_. In the Lacertilia the pineal eye, if it be an eye, is better developed than in any existing vertebrate, though even in them there is no evidence of its being used for sight. Behind the so-called pineal eye and its stalk is the _epiphysis_ or pineal body, and sometimes there is a dorsal sac between them (see fig. 18).[1] The middle or soft commissure appears in certain reptiles (_Crocodilia_ and _Chelonia_), as does also the _corpus mammillare_ (Edinger, Senckenberg, _Naturf. Gesell._ Bd. xix., 1896, and Bd. xxii., 1899; Haller, _Morph. Jahrb._ Bd. xxviii., 1900, p. 252). Among the birds there is great unity of type, the cerebellum is large and, by its forward projection, presses the optic lobes down toward the ventro-lateral part of the brain. The cerebral hemispheres are also large, owing chiefly to the great size of the _corpora striata_, which already show a differentiation into caudate nucleus, putamen and globus pallidus. The pallium is reptilian in character, though its cortical area is more extensive. The geniculate bodies are very large (Bumm, _Zeits. wiss. Zool._ Bd. xxxviii., 1883, p. 430; Brandis, _Arch. mikr. Anat._ Bd. xli., 1893, p. 623, and xliii., 1894, p. 96, and xliv., 1895, p. 534; Boyce and Warrington, _Phil. Trans._ vol. cxci., 1899, p. 293).