PARTS DERIVED FROM THE FORE-BRAIN 315 



Stratum cinereum of superior corpora quadrigemina. 

 Nucleus of inferior corpora quadrigemina. 

 Interpeduncular nucleus. (Gray.) 



Parts Derived from the Fore-brain (Prosencephalon) 



The prosencephalon is subdivided into the diencephalon, 

 or thalamic portion, and the telencephalon. 



The parts found under a description of the diencephalon 

 include the thalamus, the pineal body or epiphysis, the external 

 geniculate body and ganglion habenulse the posterior commissure, 

 the pars mammillaris hypothalami, the corpora albicantia and 

 posterior perforated space. 



The thalami (optic thalami) are two ovoid ganglionic masses, 

 consisting externally of white and internally of gray. They 

 are best seen after the removal of the overlying structures 

 the corpus callosum, the fornix, and velum interpositum 

 and rest upon (ventral surface) the tegmentum of the crura; 

 and the central gray substance of the third ventricle. 



The mesial surfaces have between them the third ventricle; 

 the middle commissure fuses each with the other in 90 per 

 cent, of the cases; these surfaces are covered by ependyma. 

 Its dorsal limit is marked by an ependymal ridge the tsenia 

 thalami, fortified by a subjacent narrow band of fibers called 

 the stria medullaris, which may be traced to the habenular 

 nucleus and habenular commissure (of the pineal body). Caudad 

 is a depression triangular area the trigonum habenulse, situated 

 cephalad of the superior corpora quadrigeminal body. The 

 dorsal surface (a portion) is in relation with the reflection 

 of the ependyma of the lateral ventricle before it enters into 

 the formation of the plexus of the lateral ventricle; the velum 

 interpositum is in relation with the rest of this surface not 

 lined by ependyma. This surface is of a faint, whitish color 

 due to a thin layer of white fibers, the stratum zonule. The 

 tsenia semicircularis is seen laterally separating this surface 

 from the caudate nucleus. Three eminences are seen the 

 tuberculum anterius, medialis, and lateralis. The anterius 

 is bulged and forms the boundary of the foramen of Monro, 

 the aperture of communication between the lateral and third 

 ventricles. The caudal extremity is rounded and overhangs 

 the brachia of the corpora quadrigemina and is called the 



