Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 fig. 284. Brain of a Ckelonian (after Bojanus). B Of a Bird. Vertical median sections. I Prosencephalon. Ill Mesencephalon. IV Metencephalon. V Myelen- cephalon. ol Olfactory, o Optic nerve, h Hypophysis, a (in A) connection between the two hemispheres of the mesencephalon, c Anterior commissure. This condition connects theReptilia with the Aves, which are distin- guished by the great proportionate size of their prosencephalon, the hemispheres of which are often greatly broadened out. They
Elements of comparative anatomy (1878) Elements of comparative anatomy elementsofcompar00gege Year: 1878 fig. 284. Brain of a Ckelonian (after Bojanus). B Of a Bird. Vertical median sections. I Prosencephalon. Ill Mesencephalon. IV Metencephalon. V Myelen- cephalon. ol Olfactory, o Optic nerve, h Hypophysis, a (in A) connection between the two hemispheres of the mesencephalon, c Anterior commissure. This condition connects theReptilia with the Aves, which are distin- guished by the great proportionate size of their prosencephalon, the hemispheres of which are often greatly broadened out. They are con- nected by a fine anterior commissure (Fig. 284, B c), and enclose a gan- glionic mass, which projects inwards from the side wall, and convert- ing the primitive cavity into a narrow space which is covered over by the thin-walled roof of the hemispheres, itself forms the largest part of the prosencephalon. These masses may be observed in as low forms as the Amphibia, and in the Eeptilia they are very large (Fig. 286, A st). The small thalamencephalon, which is completely covered over by the hemispheres of the prosence- phalon, has its roof divided. The mesencephalon, which is very large in the embryo, is divided into two pieces, which are pushed down to the sides of the brain (Fig. 285, c), and have the general internal cavity continued into them. The large median portion of the cerebellum is transversely laminated, and, owing to its size, covers over the whole of the myelencephalon. § 382. In the Mammalia the brain closely resembles that of the lower forms in its earliest stages only (cf. Fig. 280), for, owing to its special line of differentiation, it is very different to that of Birds and
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