nn: ORGANS OP Tin: 01 OB QERM-LATBB. 113 



w, is the temporal lobe (schl.l < u'ion lying above and 



conneciini: the tu<> is tin- parietal lobe (achei.l). A prominence 

 which is (level")) .1 from tin- ring-lobe backward becomes the occipital 

 lobe (hi). 



The hilt-mi ventricle has also become a 1 ' 



external form of each hemisphere (fig. 253). It also assume 

 shape of a halt'-rinir. which lies above ami Is the corpus 



striatuin (cst) that part of the wall of tliu vesicle which is forced 

 inward by t he fissure of SM.MCS. Subsequently. \\ ^dividual 



lobes of the hemispheres are more sharply dill, n-ntiated from one 

 MI, the lateral vent rid. a \^o undergoes a subdivision correspond- 

 ing to the lobes. It becomes slightly enlarged at both end-, in front 

 into the anterior cornu occupying the frontal lobe, behind and below 

 into the inferior cornu of the temporal lobe. Finally, from the half- 

 ring there is developed a small evaluation, the posterior cornu, 

 which extends backward into the occipital lobe. The region lying 

 between the horns is narrowed and becomes the cella mulia. 



All the fissures hitherto mentioned, except that of SYLVIUS, are 

 developed on the plane [median] surface of the vesicle of the 

 hemispln 



At a very early stage in Man in the tifth week (His) there arise 

 on this wall of the hemisphere two furrows running almost parallel 

 with the edge or bend of the mantle, the arcuate or hippocampal fissure 

 and the fissure of the choroid plexus (fasura hippocampi and^/waura 

 cJwroidea) ; both conform very closely in their direction to the ring- 

 lobe, and, like it, with crescentic form embrace from above the stalk 

 part of the cerebrum, the corpus striatuin. Ti :i at the 



foramen of MONRO and extend from there to the tip of the temporal 

 lobe, forming the boundaries of a region known as the marginal arch 

 (Randbogen); this projects as a thick, ning on the median surface of 

 the hemisphere, and takes part in the development of the commissural 

 system. The imaginations of the median wall of the ventricle, caused 

 by the fissures, the hippocampa I fold and the/o Id of MM lateral charoid 

 plexus, are best understood by removing in an embryo the lateral 

 wall of the hemisphere, so that one can survey the inner surface of 

 the median wall of the still very spacious and ring-like lateral 

 ventrick (fig. 253). The cavity is then seen to be partly filled with 

 a reddish frilled fold (((''/), which lies in the form of a crescent on the 

 upper surface of the corpus striatuin (ex/). In the region of the fold 

 the wall of the brain undergoes changes similar to those in the roof 

 of the medulla oblongata and of the vesicle of the between-brain 



