i8o ZOOTOMY. 



XXVII. Carefully cut into the cerebral hemisphere and^ 

 optic lobe of one (say the left) side,'- and remove^' 

 the roof of the cavities exposed : observe : 



242. The optic ventricle (Fig. 45, a), a small cavity in 

 the thick-walled optic lobe : in its inner wall is a small 

 aperture {o.v), which leads from the aqueduct of Sylvius 

 (§ 246). 



243. The lateral ventricle, a considerable cavity 

 in the cerebral hemisphere, extending in front into the 

 olfactory lobe : its dorsal and inner walls are thin ; its ventro- 

 lateral wall is greatly thickened so as to form a well-marked 

 eminence, the corpus striatum [c.s). 



244. The choroid plexus {ch.p), a plaited fold of con- 

 nective tissue, abundantly supplied with blood-vessels, lying 

 in the postero-internal angle of the lateral ventricle. 



245. Traced downwards, the choroid plexus is seen to 

 pass through the foramen of Monro (Z), f.m), a small 

 aperture in the posterior part of the inner wall of the lateral 

 ventricle, and communicating with the third ventricle 

 (§ 248) : to see it the corpus striatum must be drawn aside. 



XXVIII. Remove the left half of the cerebellum and 

 enough of the left optic lobe and cerebral hemi- 

 sphere to bring into view 



246. The aqueduct of Sylvius (ag.s), a passage 

 bounded below by the crura cerebri and above by the optic 

 lobes, in free communication with the fourth ventricle pos- 

 teriorly, and communicating by the small lateral apertures 

 already seen (§ 242) with the optic ventricles, with which it 

 forms the ventricle of the mid-brain, or mesoccele. 



247. The optic thalami, paired masses of which the 

 thalamencephalon is composed. 



' If another specimen is to be dissected, tbis may be done on both 

 sides, and a longitudinal section (§ XXIX) made of the second brain. 



