178 ZOOTOMY. 



a.c, anterior commi; sure : aj.s, aqueduct of Sylvius: cb, cerebellurao^ 

 c.c, crura cerebri : c.h, cerebral hemispheres ; ch.p, choroid plexus : c^^K 

 corpus striatum : f.m, foramen of Monro ; inf, infundibulum ; m.o, 

 medulla oblongata : o. c, optic chiasma : o. I, optic lobes : olf, olfactory 

 lobes : o.t, optic tracts : o.v, aperture between aqueduct of Sylvius 

 and optic ventricle : p.i:, posterior commissure : pn, pineal body ; ply, 

 pituitary body : i/.3, third ventricle : v.i,, fourth ventricle : / — XII, 

 cerebral nerves, 



223. The cerebellum {cb), a small semicircular flap 

 covering the anterior part of the medulla oblongata on the 

 dorsal side. 



224. The fourth ventricle (r'.4), a cavity on the 

 dorsal surface of the medulla, roofed over in front by the 

 cerebellum, but for the rest of its extent covered only by 

 the pia mater, a delicate membrane investing the brain 

 and spinal cord. 



225. The optic lobes, or corpora bigemina {p.l), 

 two large rounded elevations on the dorsal surface of the 

 brain, immediately in front of the cerebellum : they consti- 

 tute the dorsal portion of the mid-brain, the ventral 

 region of which answers to the crura cerebri {c.c). 



226. The cerebral hemispheres {c.li), large, pyramidal 

 paired masses, immediately in front of the optic lobes, 

 against the anterior faces of which they abut closely : they 

 are in close contact with one another by their flat inner 

 faces, and are pointed in front. 



227. The olfactory lobes {olf) paired, club-shaped 

 bodies continued forwards from the anterior ends of the 

 cerebral hemispheres : from their dilated anterior ends are 

 given off the olfactory (first cerebral) nerves to the nasal 

 sacs. 



228. The pineal body (/«), a small, rounded mass in 

 the middle line of the dorsal surface of the brain, at the 

 junction of the cerebral hemispheres and optic lobes. 



229. The pituitary body (/()■), a rounded mass situated 



