362 



THE CEREBRAL HEMISPHERES. 



t/io. 



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



by a wide foramen of Munro 

 ^ 2 with the third ventricle (fig. 



260). They grow rapidly in size, 

 and extend, es^yecialli/hackivards, 

 and gradually cover the thala- 

 menceplialon and the mid-brain 

 (fig. 258 1,/). The foramen of 

 Munro becomes very much nar- 

 rowed 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 ven- 

 tricle, giving to it a somewhat 

 semilunar form, the two horns 



of which constitute the permanent anterior and descending coruua 



of the lateral ventricles (fig. 262 st). 



With the further growth of the hemisphere the corpus striatum 



Fig. 258. Brain of a three months' 



HUMAN EMBRYO : NATURAL SIZE. (riom Kol- 



liker.) 



1. From above with the dorsal part of 

 hemispheres and mid-brain removed; 2. 

 From below. /. ante rior part of cnt wall of the 

 hemisphere; /'. coiiiu ammonis ; tho. optic 

 thalamus; est. corpus striatum; to. optic 

 tract; cm. corpora mammillaria; ^;. pons 

 Varolii. 



-•■yfrf 



■str 



FiG. 259. Transverse section through the brain oe 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; amin. cornu ammonis (hippo- 

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

 lucidum; frx2. vertical fibres of the fornix; c»w. anterior commissure; trm. lamina 

 terminalis; str. corpus stiiatum; ///'. nucleus lenticulari-i of corpus striatum; vtr 1. 

 , lateral ventricle; otr'6. third ventricle; /7J/. slit between cerebral hemispheres. 



