338 



DLVELOPMENT OF THE HUMAN BRAIN 



upper and posterior margin of this ventricle the ' Pineal 

 body' soon appears, and also its * peduncles ' which extend 

 forwards on each side. 



By the 12th week of intrauterine 

 life, the configuration of the Brain has 

 undergone a very marked change ; first 

 by reason of the increased size of the 

 Cerebellum, (fig. 123, C, c) which is now 

 thicker and marked by a median longi- 

 tudinal furrow, though otherwise smooth 

 on its surface; and, secondly, by the still 

 more striking development of the Cere- 

 bral Hemispheres (C, a), which have 

 already grown so much backwards as com- 

 pletely to overlap the ' third ventricle ' 

 (fig. 123, F, 8). On the under surface of 

 each Hemisphere an Olfactory Lobe is 

 now very distinct, as a hollow bud-like 

 outgrowth, the cavity of which is con- 

 tinuous with that of the Hemisphere 

 from which it projects. 



The ' lateral ventricles ' themselves 



Fi<;. 12.0.— Br;iin and ,. ..■, .■, •, 



SpiiMi Cord. .fa Foetus of are, morcovcr, continuous with the cavity 

 Four Months, seen from ^f ^j^g Thalameucephalon, or ' third ven- 



behiud. (Sliarpey, after . i • n /? 



Koiiikcr.) /,, Hemi- tricle,' byau opening on each side ot 

 spheres of the Cerebrum;. ^utorior extremity, kuown bv the 



VI, coipora quadnge- "^ w^xi^v^ v-. j, 



muia; c, cerebeUum ; name of the ' foramcii of Muiiro.' Near 



tu o, medulla oblongata, , . • , i i i • a 



the fourth ventrieie be- tlus opeuiug a trausvcrsc band begins to 

 ing overlapped by the appear (abovo and in front), which 



CereljcUum ; .<; x, the cer- ^ ^ ^ ^ • i j • 



vicai and lumbar swell- conuccts tlic two hemispheres and is 

 ings of the spinal eord. ^^^^^^^,^1^^ ^^ corrcspoiid with the Com- 

 mencement of the great transverse commissure, the Corpus 

 Callosum, and perhaps also with the Anterior Commis- 

 sure. The walls of the Cerebral Hemispheres are very 



