. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 2-_>6 COMPARATIVE ANATOMY (Primates) even part of the cerebellum is hidden (Figs. 173, A and B), although this is to a greater extent the case in some of the lower Apes, with smooth hemispheres ( Hapale, Chrysothrix), than in Man. No satisfactory explanation has so far been given for the different degrees of convolution seen amongst Mammals: as a general rule, the brain in lower and smaller types (except, in Echidna) is less convoluted than in higher and larger ones. The number of fibres radiating from the cor
. Comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates. 2-_>6 COMPARATIVE ANATOMY (Primates) even part of the cerebellum is hidden (Figs. 173, A and B), although this is to a greater extent the case in some of the lower Apes, with smooth hemispheres ( Hapale, Chrysothrix), than in Man. No satisfactory explanation has so far been given for the different degrees of convolution seen amongst Mammals: as a general rule, the brain in lower and smaller types (except, in Echidna) is less convoluted than in higher and larger ones. The number of fibres radiating from the cortex (corona radiata) is very small in lower types ( Rodents), and largest in Man. A complex network of fibres in the cortex itself connects its various parts together, and other strong bundles extend through the MH. Jiff FIG. 173A.—HUMAN BRAIN. Median longitudinal vertical section. (Mainly after Reichert.) corpus callosum ; G, fornix, which extends antero-ventrally to the lamina terminalis (Col), in the upper part of which is seen the anterior commissure (Ca), and between the latter and the optic thalami (To) the foramen of Monro (FM) ; H, pituitary body ; ////, cerebellum ; MH, corpora bigemina, with the iter (Aq], anterior to which is seen the posterior commissure (Cp); NH, medulla oblongata, with the pons Varolii (P) ; -ff, spinal cord; T, infundibulum ; Teh, tela choroidea ; To, optic thalamus (diencephalon), with the middle commissure (Cm); VH, cerebral hemisphere; Z, pineal bod}'; /, olfactory nerve ; //, optic nerve. hemispheres connecting individual regions of the pallium with one another. The commissures between the hemispheres known as the corpus callosum and fornix (Fig. 173, A) are also much more highly developed than in other Vertebrates. The former is an important structure in the higher Mammalia, its development corresponding to that of the pallium: ifc extends upwards and then backwards from the region of the lamina terminalis in the form of a thin plate,
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