EMBRYOLOGY AND COMPARATIVE ANATOMY OF BRAIN. 



15 



into the simple layer of epithelium is called the margin of the 

 hemisphere. This margin is, at a later period, clearly marked 

 throughout its entire length by a bundle of white fibres, the 

 fornix. 



After the most important portions of the human cerebrum 

 have begun to develop, it 

 has the appearance repre- 

 sented in the accompany- 

 ing Fig. 7. It has grown 

 out backward and bent 

 downward. At the point 

 where the corpus striatum 

 (which will be mentioped 

 later) is situated inter- 

 nally, the outer wall has 

 not expanded so rapidly as 

 in the other regions of the 

 hemispheres; so that there 

 has developed or, rather 

 remained a depression, 

 the fissure or fossa of 

 Svlvius. There can now 



* 



be easily distinguished an 

 anterior or frontal lobe, a 

 posterior or occipital lobe, 



j-i-irl l^r>f-r>/->n fli/- 

 OCl \\CC11 Hie 



. . 1 , brain vesicle and the rudiment of the corpus striatum. 



parietal lobe. lliat part Observe the prolongation of the cortical layer into 



the latter, and see how it covers both the inner and 



of the hemisphere which outer surf ace_s. 



Pnmare Scheidewana , Primary division-wall. 



lies below the fissure of 



Sylvius is called the temporal lobe. Internally the hemispheres 

 are hollow, and naturally their cavities conform to the general 

 shape of the brain. That part of the ventricle which lies in the 

 frontal lobe is called the anterior horn, that which lies in the 

 ocripital lobe the posterior horn, and that which lies in the tem- 

 poral lobe the inferior horn. At this stage of development the 



r^, Frontal section through the head of a human em- 



G a brypof2%months. Shows the involution of the fore- 



