248 



THE NERVOUS SYSTEM 



invaginated into the ventricle, pushing this epithelial layer before it and con- 

 stituting the chorioid plexus. 



The posterior horn, or cornu posterius, extends into the occipital lobe of 

 the human brain, tapering to a point, and describing a gentle curve with con- 

 cavity directed medially (Figs. 177, 181). 



The tapetum of the corpus callosum forms a thin but distinct layer in the 

 roof and lateral watt of the posterior horn, and is covered in turn by a thicker 

 layer of fibers belonging to optic radiation or radiatio occipitothalamica (Fig. 

 190). In the medial wall two longitudinal elevations may be seen. Of these, 



Corpus callosum 



Head of caudate 

 nucleus " 



Body offornix--^ 



Fimbria of hippo- 

 campus 



Hippocampus - 



Splenium of corpus 

 callosum 



Anterior horn of 

 lateral ventricle 



Thick portion of 

 septum pellucidum 



~ Lateral fissure 



Interventricular 

 foramen 



- Lateral ventricle 



Fig. 178. Dissection of the telencephalon of the sheep to show the lateral ventricle and the 

 structures which form its floor. Dorsal view. 



the more dorsal one is known as the bulb of the posterior horn (bulbus cornu), 

 and is formed by the occipital portion of the radiation of the corpus callosum 

 or forceps major. The other elevation, known as the calcar avis, is larger and 

 is produced by the rostral part of the calcarine fissure, which here causes a fold- 

 ing of the entire thickness of the pallium (p. 238). 



The inferior horn, or cornu inferius, curves ventrally and then rostrally into 

 the temporal lobe (Fig. 181). The angle between the diverging inferior and 

 posterior horns is known as the collateral trigone. This horn lies in the medial 

 part of the temporal lobe and does not quite reach the temporal pole. The roof 



