354 NERl^OUS SYSTEM. 



covered by the caudally projecting part of the cerebral hemi- 

 spheres. The medial larger end of each thalamus is near the 

 middle line; thence the thalamus extends caudolaterad, and 

 rises at its lateral extremity into a sharply rounded projection, 

 the corpus geniculatum laterale (.r). From this projection the 

 thalamus is continued ventrad and then craniomediad as a large 

 band of fibres, the Optic tract (tractus Opticus) (Fig. 142, ^/), 

 which extends to the optic chiasma (e), where it passes into the 

 optic nerves {/). On the caudal border of the thalamus, near 

 the median line, is a very faint projection, the pulvinar (Fig. 

 141 , w) ; this lies just craniad of the lateral border of the cranial 

 corpus quadrigeminum (q). Just ventrad of the corpus genicu- 

 latum laterale (.t-) is the prominent rounded corpus geniculatum 

 mediale (s); this is connected by a prominent ridge, the 

 brachium quadrigeminum inferius (r), with the caudal corpus 

 quadrigeminum (/). In a similar manner the brachium 

 quadrigeminum superius passes from the cranial corpus quad- 

 rigeminum {q) into the thalamus itself. 



Between the two thalami there exists a groove, the sulcus 

 hypothalamicus. Over this groove lies the roof of the third 

 ventricle, forming the choroid plexus of the third ventricle 

 (Fig. 143, w). The medial surface of the two thalami are flat 

 and extend directly ventrad, forming part of the lateral 

 boundary of the third ventricle (Fig. 143, //). The two 

 medial surfaces meet over a considerable area across the narrow 

 cavity of the third ventricle, and unite, forming the massa 

 intermedia (Fig. 143, /") or intermediate mass of the thalamus 

 (" middle commissure "). This connection of the thalami of 

 the two sides is thus not a primitive one, forming no part of 

 the roof or floor of the central cavity, but is a secondary con- 

 nection due to a growing together of a part of the two sides of 

 the ventricle across its cavity. Along the dorsal edge of the 

 medial border of each thalamus passes a distinct white strand, 

 the stria medullaris (Fig. 141, 7/); the two stria; meet in an 

 arch caudad, lying beneath the pineal body (2). 



The thalamus is separated craniolaterad by a groove ( 1 ) 

 from the corpus striatum (j), on the floor of the cerebral 

 hemisphere. 



