844 



THE NERVOUS SYSTEM 



This comprises — (1) the mammillary bodies [corpora mammillaria] (albicantia), 

 the two rounded projections situated in the anterior part of the interpeduncular 

 fossa, and (2) the anterior portion of the posterior perforated substance or the 

 small triangle of grey substance forming the floor of the posterior part of the 

 third ventricle, and which represents numerous openings for the passage of 

 branches of the posterior cerebral arteries (fig. 668). The hypothalamic portions 

 of the cerebral peduncles might be included. The structures of the optic or re- 

 maining portion of the hypothalamus belong to the telencephalon. 



The upper or dorsal surface of the diencephalon is completely overlapped and 

 hidden b}" the telencephalon, and covered by the intervening ingrowth of the 



Fig. 665. 



-Dorsal Surface of Diencephalon with Adjacent Structures. 

 (After Obersteiner.) 



Anterior cornu of 

 lateral ventricle 



Fifth ventricle 

 Septum pellucidum 



Columns of fornix 



Stria terminalis 

 Anterior commissure 



Third ventricle 



Massa intermedia 

 Chorioidal sulcus 



Superior colliculus 



Medial geniculate 

 body 



Lateral sulcus of mes- 

 encephalon 



Brachium of pons 



Acustic medullary stria 



Median sulcus 



Eminence of hypoglossal 



Restifcrm body 



Clava 



Posterior fissure 



Postero-intermediate sulcus 



Postero-lateral sulcus 



Corpus callosum 



Caudate nucleus 



Interventricular fora- 

 men (.Monroij 



Anterior tubercle of 

 thalamus 



Medullary stria of 

 thalamus 



Habenular commissure 

 Epiphysis 



Sulcus Corp. quad, 

 medialis 



Inferior colliculus 



Frenulum veli 



Lingula cerebelli 



Eminence of facial 

 and abducens 



Acoustic area 

 Trigonum vagi 



— Tuberculum cuneatum 

 Funiculus gracilis 

 Funiculus cuneatus 



— Lateral funiculus 



cerebral meninges, the tela chorioidea of the third ventricle (velum interpositum). 

 These removed (fig. 665), it is seen that the thalami on cither side are by far the 

 most conspicuous objects of the dienceplialon. They, together with the parts 

 developed in connection with them, are distinguished as the thalamencpehalon. 

 Th(! thalamencephalon consists of — (1) the thalami; (2) the meiathalamus or 

 geniculate bodies; and (3) the epithalamus, comjirising the epiphysis with the 

 posterior commissure V)elow it and the habenular trigone on either side. 



The thalami arc two ovoid, couch-like masses of grey substance which form 

 the lateral walls of the third ventricle. The cavity of the ventricle is narrow, and 

 quite frequently the thalami arc continuous through it across the mid-line by a 

 small but variable neck of grey substance, the massa intermedia ("middle com- 

 missure"). The upper surfaces of tiie thalami aro free. Tiie edges of the tela 

 chorioidea of the third ventricle are attaclied to tiie lateral part of the surface of 

 each tlialamus, and, when removed, leave the Imnia chorioidea lying in the chori- 



