BRAIN 



387 



ately in front of the mid-brain. Its sides are thick and are known as 

 the thalami ; its roof and floor are thin. The floor is prolonged 

 into a hollow structure known as the infundibulum, which, 

 with a glandular, non-nervous mass called the hypophysis, makes 

 up the pituitary body. The roof is prolonged into a short hollow 

 stalk, which in the tadpole is connected with a structure known 

 as the pineal body. In the adult this has become separated and 

 lies outside the skull. In certain other animals the pineal body is 

 much more highly developed and still connected with its stalk, 

 and its structure shows that it is the remnant of a middle eye, 



olfactory 

 / /obes^ 



cerebra/ 

 hemisph. 



optic 

 thalami 



pineal 

 body 



optic _ 

 /obes 



C9r»bf/' 

 lum 



medulla 

 oblongata. 



\st 



\'i lateral 

 \ vtntrici* 



' ^nd 



for/smen 

 'rr~of Monro 



^^ 3rd . , 

 ventric/e 



aqueduct 

 ■ of 

 Syl ius 



'- 4M 

 yentric/f 



hypophysis 

 infundibulum 



Fig. 303. — Brain of a frog. — From Thomson, after Wiedersheim. 



7, Dorsal Aspect ; II, Ventral Aspect (the numbers indicate the origins of the nerves) ; 



///, Horizontal Section. 



though it is no longer functional. In front of the pineal stalk 

 lies an anterior choroid plexus. The cavity of the thalamen- 

 cephalon is deep but narrow, and is known as the third ventricle. 

 It is bounded in front by a wall known as the lamina terminalis. 

 Behind this on each side an opening known as the foramen of 

 Monro or foramen interventriculare leads into the cavity or 

 lateral ventricle of one of the cerebral hemispheres. These are 

 oblong-oval bodies narrowing forwards to join a mass which is 

 indistinctly separated into two olfactory lobes. The median walls 

 of the cerebral hemispheres touch in front and behind, but for a 

 considerable distance they are quite separate. Two regions may 

 be distinguished in the wall of each cerebral hemisphere — the 

 ventrolateral region, which is thickened and is known as the 

 corpus striatum, and the rest of the wall, which is the pallium. 



