LEPUS CUNICULUS 351 



geniculate body and the anterior quadrigeminal bodies. Certain 

 parts of the lamina terminalis, namely, the anterior commissure, 

 the septum lucidum, the fornix and the corpus callosum, we have 

 already considered ; but there still remains a small, almost unaltered 

 portion of it at the anterior end of the ventricle. This runs from the 

 anterior commissure downwards and backwards to the optic chiasma, 

 and to this the term lamina terminalis in the limited sense may be 

 applied. The chiasma projects into the floor of the ventricle, leaving 

 a small pre-optie recess in front of it, whose floor is formed by the 

 lamina. The remaining structures in the floor of the third ven- 

 tricle have already been considered. 



Mid -Brain. 



The mid-brain occupies but a small part of the total brain 

 mass in the adult and its cavity, the iter a tertio ad quartum ventri- 

 culum or aqueduct of Sylvius, is reduced to a short narrow passage 

 which is roofed by the quadrigeminal bodies and has its side walls 

 formed by the crura cerebri. The anterior quadrigeminal bodies or 

 colliculi superiores are fairly large oval masses, and much larger 

 than the posterior. Each gives off two white bands of fibres, an 

 anterior brachium, which passes forwards and downwards behind 

 the pulvinar into the optic tract, and a posterior brachium, which 

 passes down to disappear under the internal geniculate body. The 

 posterior quadrigeminal bodies or colliculi inferiores are small 

 structures underlying the former, and each gives off a small brachium 

 which can be traced forward to the posterior part of the corona 

 radiata. 



The crura or pedunculi cerebri are two large masses running 

 backwards from under the hemispheres and coming out between the 

 hippocampal lobules., They pass backwards from the optic 

 chiasma, visible on the ventral surface as two wide pillars, and leaving 

 between their anterior ends the posterior perforated spot, and they 

 disappear beneath the pons. As noted, they are extremely thick, 

 and constitute the side walls and floor of the iter. 



Hind-Brain, 



The visible dorsal surface of the hind-brain is composed 

 entirely of the cerebellum. In the middle line this is constituted 

 by a median longitudinal portion termed the vermis, the surface of 

 which is marked by a number of close-set transverse sulci. At its 

 lateral border is a longitudinal fissure separating it from the lateral 

 lobe of the cerebellum, or hemisphserium cerebelli. This in its turn 

 has attached to its ventro-lateral border a small lateral lobe, the 



