. The development of the chick; an introduction to embryology . atter antl develop relatively late (aboutsixteen days, Ramon y Cajal). 111. TiiK Development of the Brain Unfortunately the later development of the ])i-ain of birdshas not been fully studied. The following account is thereforefragmentary. It is based mainly on a dissection and sections ofthe brain of chicks of eight days incubation. Fig. 147 is a drawing of a dissection of the brain of an eight-day embryo. The left half of the brain has l)een removed, andthe median wall of the right cerebral hemisphere also. Thedetails of the cut
. The development of the chick; an introduction to embryology . atter antl develop relatively late (aboutsixteen days, Ramon y Cajal). 111. TiiK Development of the Brain Unfortunately the later development of the ])i-ain of birdshas not been fully studied. The following account is thereforefragmentary. It is based mainly on a dissection and sections ofthe brain of chicks of eight days incubation. Fig. 147 is a drawing of a dissection of the brain of an eight-day embryo. The left half of the brain has l)een removed, andthe median wall of the right cerebral hemisphere also. Thedetails of the cut surfaces are drawn in from sections. Iigs. 148 THE NERVOUS SYSTEM 245 and 150 show median and lateral sagittal sections of the samestage. The flexures of the brain at this stage are: (1) the cranialflexure marked by the plica encephali ventralis on the ventralsurface, (2) the cervical flexure at the junction of myelencephalonand cord, somewhat reduced in this stage, and (3) the pontineflexure, a ventral projection of the floor of the myelencephalon. Cowpast-. ~ ^ /?o/? o/A Fig. 147. — Dissection of the brain of an 8-day chick. For description seetext. The arrows shown in the figure lie near the dorsal and ventral boun-daries of the foramen of Monro,ch. PI., Choroid plexus. Com. ant., Anterior commissure. Com. post.,Posterior commissure. C. Corpus striatum. Ep., Epiphysis. H.,Hemisphere. Hyp., Hypojjhysis. L. t., Lamina terminalis. Myel., Myel-encephalon. olf., Olfactory nerve, op. N., Optic chiasma. op. L., Opticlobe. Par., Parapliysis. Paren., Parencephalon. pi. ene. v., Plica en-cephali ventralis. pont. Fl., Pontine flexure. Rec. op., Recessus Inf., Saccus infundibuli. Tel. Telencephalon medium. Th., Tha-lamus. T. Torus transversus. Tr., Commissura trochlearis. The lines a-a, h-h, c-c, d-d, e-e, f-f, represent the planes of section A,B, C, D, E, and F of Fig. 151. Telencephalon. The telencephalon is bounded jiostoriorly,as noted in the last
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