302 



THE CERE BRA L HEMISPHERES. 



The hemispheres contain at fir^t very large cavities, communicating 



by a wide foramen of Munro 



j 2 with the third ventricle (tig. 



2(JO). They grow rapidly in size, 

 and extend, especially back wards, 

 and gradually cover the thala- 

 mencephalon and the mid-brain 

 (fig. 2-38 I,/). The foramen of 

 Munro becomes very much nar- 

 rowed and reduced to a mere 

 slit. 



The walls are originally 

 nearly uniformly thick, but the 

 rloor becomes thickened on each 

 side, and gives rise to the corpus 

 striatum "(figs. 2(30 and 261 st). 

 The corpus striatum projects 

 upwards into each lateral ven- 

 tricle, giving to it a somewhat 



FIG. 258. BRAIN OF A THREE MONTHS' 

 HITMAN EMBRYO: NATURAL SIZE. (From Kol- 

 liker.) 



1. From above with the dorsal part of 

 hemispheres and mid-brain removed ; 2. 

 From below. /'. antt rior part of cut wall of the 

 hemisphere; /". coinu ammonis; th<>. o]itic 

 thalamus; cat. corpus striatum; t. optic 

 tract; cm. corpora mammillaria ; p. pons 

 Varolii. 



semiluuar form, the two horns 



of which constitute the permanent anterior and descending corriua 

 of the lateral ventricles (fig. 262 ,s^). 



With the further growth of the hemisphere the corpus striatum 



/tsns 



-rtr, 



FIG. 251). TRANSVERSE SECTION THROUGH THE BRAIN OF A BABBIT OF FIVE 

 CENTIMETRES. (After Mihalkovics.) 



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

 immediately in fiont of the foramen of Munro. 



Inns, cerebral hemispheres; cal. corpus callosum; nmm. cornu ammonis (hippo- 

 campus major); cm*, superior commissure of the cornua ammonis; xpt. septum 

 lucidum; frx 2. vertical fibres of the fornix; emu. anterior commissure; tnn. lamina 

 terminalis; xtr. corpus stiiatum; /(/'.nucleus lenticular^ of corpus striatum; rtr i. 

 lateral veiitiicle; ctr'A. tliird ventricle; ///. slit between cerebral hemispheres. 



