'368 THE BRAIN 



which separates it from the inferior part of the inferior 

 temporal gyrus (Fig. 138). 



When the survey of the inferior surfaces of the cerebral 

 hemispheres is completed, the inferior aspect of a brain, or 

 a cast, in which the mid- and hind-brain sections are still in 

 situ, or in which they can be replaced, should be examined. 



When that is done it will be noted that the posterior 

 sections of the inferior surfaces of the hemispheres are 

 concealed by the cerebellum, but the more anterior parts of 

 the inferior surfaces are still visible. Between the anterior 

 parts of the inferior surfaces, in the median plane, is the 

 anterior part of the longitudinal fissure. Behind the 

 anterior part of the longitudinal fissure lies the optic chiasma, 

 but if the chiasma is carefully turned backwards, the lamina 

 terminalis will be seen passing upwards and forwards into the 

 longitudinal fissure (Fig. 162). At its antero-lateral angles 

 the optic chiasma receives the optic nerves, and from each 

 postero-lateral angle it gives off an optic tract, which runs 

 postero-laterally and disappears from view under cover of 

 the piriform area. 



Behind the optic chiasma is the tuber cinereum with the 

 infundibulum projecting from its apex to connect it with the 

 hypophysis. Behind the tuber cinereum lie two round white 

 bodies called the corpora mamillaria, and still more posteriorly 

 is the deepest part of the interpeduncular fossa, which lies 

 between the medial borders of the pedunculi cerebri. The 

 superior boundary of the interpeduncular fossa is the posterior 

 perforated substance. 



The pedunculi cerebri run upwards, forwards and laterally, 

 at the sides of the interpeduncular fossa. The upper end 

 of each disappears into the base of the corresponding hemi- 

 sphere, and its lower end is continuous with the pons of the 

 hind-brain. 



Springing from the medial side of each pedunculus is the 

 corresponding oculo- motor nerve, and curving round its 

 lateral side is the trochlear nerve. 



Below the pedunculi cerebri of the mid-brain is the pons 

 of the hind-brain, which is connected, on each side, with the 

 corresponding hemisphere of the cerebellum. 



Springing from each side of the pons, immediately medial to 

 the corresponding hemisphere of the cerebellum, are the motor 

 root and sensory root of the trigeminal nerve of that side. 



