ANIMAL BIOLOGY. 



[Part I. 



f.c. 



the corpus striatum (Fig. 71, c. st.), which projects upwards into 



the lateral ventricles (/. v.). 

 Posteriorly the corpus stria- 

 tum comes into close relation 

 L, with the optic thalamus. The 

 outer wall of the hemisphere 

 - c. sfc. thickens, while the inner wall 

 becomes relatively thinner. 



FlO. TI.-DIAORAMMATIC SECTION OF FcETAL 



IN (after Koiiiker). 



In this inner wall two curved 



ance, and project towards the 

 c. st. Corpus striatum. c/i. pi Choroid plexus, interior of the lateral veh- 



/. c. Falx cerebri. fc. m. Hippocampus major. tric ] e< Qf these the Upper 

 I. v. Lateral ventricle. HI. Third ventricle. . . ri 



gives rise to a thickened 



mass of white nervous tissue, the hippocampus major (Fig. 71, 

 h. m.). The wall of the lower fold becomes thinned to the 

 merest film, and a vascular plexus (ch. pi.), derived from the 

 connective tissue septum between the hemispheres (falx cerebri, 

 f. c.) is formed in the fold, in the manner shown in the trans- 

 verse section of the brain of a foetal sheep (after Koiiiker) 

 Fig. 71. This constitutes the choroid plexus of the lateral 

 ventricle. It is also present in the pigeon. 



In the lamina terminalis (I. t.), besides the transverse fibres of 

 the anterior commissures (a. c. ), two vertical bands of fibres are 

 developed. These constitute the anterior pillars of the fornix 

 (f. in 69, B.). They are continued doAvnwards along the floor 

 of the third ventricle, to end in the mammillary body (c. m.). 

 Traced upwards they meet in the middle line in the roof of the 

 third ventricle, thus forming the body of the fornix. Thence 

 bands of fibres (the posterior pillars of the fornix) pass back- 

 wards, arching over the foramen of Monro, to unite with the 

 hippocampus major. 



The main commissure, uniting the cerebral hemispheres, is 

 the corpus callosum (c, ca.). It may be seen by carefully 

 separating the cerebral hemispheres on the dorsal side, and 

 constitutes a flat white band. It is seen in section in 

 Fig. 69, B. At its anterior end it bends slightly downwards 



