OPTIC THALAMUS. 



Ill 



pineal body (habenula) (Pen} lies a triangular depressed surface, separated posteriorly 

 from the mesencephalon by a transverse groove and passing mesially into the stalk 

 of the pineal body. This triangular surface is termed the trigonum habenulm. It is 

 bounded laterally by the sukus habenulce. The mesial surface of the thalamus lies 

 in the third ventricle. It is covered with epithelium and is joined with that of 

 the opposite side by the middle commissure. The posterior rounded surface is 

 occupied almost entirely by the pulvinar. Below and external to this is the outer 

 geniculate body, which is placed just above the inner geniculate body before mentioned 

 (p. 105), the two being separated from one another by one of the roots of the optic 



Fig. 82. VIEW FROM ABOVE OF THE 



THIRD VENTRICLE AND A VART OP 

 THE LATERAL VENTRICLES (Henle). 



The brain has been sliced horizontally 

 immediately below the corpus callosum, 

 and the fornix and velum interpositum 

 have been removed. 



Tho, thalamus options ; Ts, its ante- 

 rior tubercle ; Pv, pulvinar ; Com, middle 

 commissure stretching between the two 

 optic thalami across the middle of the 

 third ventricle ; Cf, columns of the for- 

 nix ; Cn, pineal gland projecting down- 

 wards and backwards between the superior 

 corpora quadrigemina ; &t, stria termi- 

 nalis ; Cs, nucleus caudatus of the corpus 

 striatum ; Vsl, ventricle of the septum 

 lucidum ; Ccl 2 , section of the genu of the 

 corpus callosum ; Pen, pineal peduncle ; 

 Tfo, pineal stria ; Cop, posterior com- 

 missure. 



tract (upper brachium) (fig. 86). 

 From this brachium and from 

 the two geniculate bodies the 

 optic tract curves downwards 

 and forwards around the crus 

 cerebri. 



The lateral and ventral sur- 

 faces of the thalamus are not 

 free, but are united with other 

 parts of the brain. The ventral 

 surface is united with a prolonga- 

 tion of the tegmental part of the 

 crus cerebri, and more anteriorly 

 the corpus albicans and the side 

 of the tuber cinereum lie below 



it. The lateral surface is covered by white substance which is formed of the fibres 

 of the crusta, which here diverge into the substance of the hemisphere, and pass 

 between the thalamus and the lenticular nucleus as the internal capsule. 



The thalami optici are covered on their free surfaces (mesial and dorsal) 

 (fig. 83), by a layer of white fibres, most marked upon the dorsal surface (stratum 

 zonale), and mainly running antero-posteriorly. On their outer surface, as just 

 mentioned, is the white matter of the inner capsule (i. c.} formed by fibres diverging 

 from the crusta into the hemispheres. Next to the thalamus on this side is a denser 

 layer of white fibres, termed the outer medullary lamina. All along this surface 

 radiating fibres pass out of the thalamus to mingle with the fibres of the inner 

 capsule and to pass with these to the surface of the cerebral hemispheres. Those in 



\ 



Pv 



