THE NERVOUS SYSTEM 245 
and 150 show median and lateral sagittal sections of the same 
stage. 
The flexures of the brain at this stage are: (1) the cranial 
flexure marked by the plica encephali ventralis on the ventral 
surface, (2) the cervical flexure at the junction of myelencephalon 
and cord, somewhat reduced in this stage, and (3) the pontine 
flexure, a ventral projection of the floor of the myelencephalon. 
| Comant. pac op 
Ze mee 
Fig. 147. — Dissection of the brain of an 8-day chick. For description see 
text. The arrows shown in the figure lie near the dorsal and ventral boun- 
daries of the foramen of Monro. 
ch. Pl., Choroid plexus. Com. ant., Anterior commissure. Com. post., 
Posterior commissure. CC. str., Corpus striatum. Ep., Epiphysis.  H., 
Hemisphere. Hyp., Hypophysis. L. t., Lamina terminalis. Myel., Myel- 
encephalon.  olf., Olfactory nerve. op. N., Optie chiasma. op. L., Optic 
lobe. Par., Paraphysis. Paren., Parencephalon. pl. enc. v., Plica en- 
cephali ventralis. pont. Fl., Pontine flexure. Ree. op., Recessus opticus. 
S. Inf., Saceus infundibuli. Tel. med., Telencephalon medium. Th., Tha- 
lamus. T. tr., Torus transversus. Tr., Commissura trochlearis. 
The lines a—a, b-b, e-e, d-d, e-e, f-f, represent the planes of section A, 
Bw. Dib rand: PofsHios) 15k 
Telencephalon. The telencephalon is bounded posteriorly, 
as noted in the last chapter, by the line drawn from the velum 
transversum to the recessus opticus. The telencephalon medium 
has grown but little since the fourth day, but the hemispheres 
