190 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



it appears early in the fifth month. It is present in all primates 

 except the very lowest. The optic radiations end in the cortex of 



.line of section 

 par-oecip. fis. 



calcctr. fis. 

 calcarauis 



calcarine fis. 



post horn 



uncus 



Fig. 155. 

 Flo. 156. 



fascia dentata 



Fit:. 150. 



-View of the Mesial Surface of the Brain in the 5th month. 

 -Section of the Occipital Lobe at the position marked in Fig. 155. 



the fissure. In Fig. 157 the condition of the occipital lobe in 

 the 4th week is shown. The cerebral vesicle has arisen as a 

 hollow protrusion from the anterior superior end of the fore-brain 

 (3rd ventricle). The lateral ventricle is as yet undifferentiated 

 into horns and only the rudiment of the occipital lobe is present. 

 The occipital lobe is produced by a backward growth of the 

 cerebral vesicle, the posterior horn being produced as a diverti- 



rudiment of occip. lobe 



olf. lobe 



optic recess 



foramen of Monro 



Fib. 157.— Mesial Section of the Brain at the 4th week shewing the Rudiment of 

 the Occipital Lobe. (After His.) 



culum of the cavity of the vesicle. By the 5th month the 

 occipital lobe has reached far enough back to overlap the 

 cerebellum. 



