440 



THE CEREBRAL HEMISPHERES. 



mid-brain (fig. 258 I,/). The foramen of Munro becomes very 

 much narrowed and reduced to a mere slit. 



The walls are originally , ^ 



nearly uniformly thick, but 

 the floor becomes thickened 

 on each side, and gives rise 

 to the corpus striatum (figs. 

 260 and 261 st). The corpus 

 striatum projects upwards 

 into each lateral ventricle, 

 giving to it a somewhat 

 semilunar form, the two 

 horns of which constitute 

 the permanent anterior and 

 descending cornua of the 

 lateral ventricles (fig. 262 st). 



FIG. 258. BRAIN OF A THREE MONTHS' 

 HUMAN EMBRYO: NATURAL SIZE. (From 

 Kolliker.) 



i. From above with the dorsal part of 

 hemispheres and mid-brain removed ; i. 

 From below, f. anterior part of cut wall of 

 the hemisphere ; f ' . cornu ammonis ; f/io. 

 optic thalamus ; cst. corpus striatum ; to. 

 optic tract ; cm. corpora mammillaria ; /. 

 pons Varolii. 



With the further growth of the hemisphere the corpus 



CftZ 



Ams 



spt. 



FIG. 259. TRANSVERSE SECTION THROUGH THE BRAIN OF A RABBIT OF FIVE 

 CENTIMETRES. (After Mihalkovics.) 



The section passes through nearly the posterior border of the septum lucidum, 

 immediately in front of the foramen of Munro. 



hms. cerebral hemispheres ; cal. corpus callosum ; amm. cornu ammonis (hippo- 

 campus major) ; cms. superior commissure of the cornua ammonis ; spt. septum 

 lucidum ; frx i. vertical fibres of the fornix; ana. anterior commissure ; trm. lamina 

 terminalis; str. corpus striatum; Iff. nucleus lenticularis of corpus striatum; vtr i. 

 lateral ventricle; vtr 3. third ventricle; ipl. slit between cerebral hemispheres. 



