THIRD VENTRICLE. 



97 



probably been formed by the detachment of some of the epithelium cells. The fibres 

 which extend from them often branch dichotomously besides possessing many small 

 lateral offsets. 



The Sylvian aqueduct expands suddenly immediately after passing beneath 

 the posterior commissure into a comparatively large, laterally compressed cavity, 

 termed the third ventricle (fig. 73). This, which is deeper in front than behind, 

 passes at its anterior and lower extremity to a conical termination which lies over the 



Fig. 73. VlEW FROM ABOVE OP THE 



THIRD VENTRICLE AND A PART OP 

 THE LATERAL VENTRICLES (Ilenle). 



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; Pe, pulvinar ; Com, middle 

 commissure stretching between the two 

 optic thalami across the middle of the 

 third ventricle ; Cf, columns of the fornix; 

 Cn, pineal gland projecting downwards 

 and backwards between the superior cor- 

 pora quadrigemina ; St, stria terminalis ; 

 Cs, nucleus caudatus of the corpus stria- 

 turn ; Vsl, ventricle of the septum luci- 

 durn ; Ccl 2 , section of the genu of the 

 corpus callosum ; Pen, commencement of 

 the pineal stria or peduncle, Tfo ; Cop, 

 posterior commissure. 



optic commissure (optic recess). 

 Below and behind this is a conical 

 -depression, the mfundibulum, 

 leading towards \h& pituitary bod)/ 

 (hypophysis cerebri). At the 

 posterior extremity, immediately 

 above the entrance of the aque- 

 duct, and separated from it by 

 the posterior commissure, is an- 

 other smaller depression (pineal 

 recess) (fig. 90, p. 126) extend- 

 ing into the stalk of the pineal 

 gland or conarium (fig. 73, Cn), 

 which here projects backwards 

 over the mid-brain. Another 

 depression extends backwards 



over the pineal stalk ; this is termed the suprapineal recess (fig. 90). The 

 ventricle is bounded laterally by the optic thalami (fig. 73, Tho), which come 

 almost in contact with one another in the median plane ; and a little in advance 

 of the middle of the ventricle, are actually united by a connecting band of grey 

 matter of variable extent, termed the middle or soft commissure (fig. 73, Com. ; 

 fig. 83, m.c.). This is sometimes double and occasionally wanting : it is liable 

 to be torn across in removing the brain. The lateral walls of the cavity are 

 slightly convex, and each is marked towards the anterior end by a white curved 

 band, with its convexity forwards, which becomes more prominent as it passes 

 upwards towards the roof. These bands are named the anterior pillars or columns 

 of the fornix (fig. 73, Cf). Immediately behind the most prominent part of 

 each of these, between it and the anterior part of the thalamus, is an aperture 

 (foramen of Monro) leading into the ventricle of the hemisphere (lateral ventricle.) 

 VOL. in. n 



