THE RABBIT. 369 



and from their lower and front surfaces are given off the 

 filaments of the first or olfactory nerve. 



485. About the centre of the base of the brain, between 

 the temporal lobes of the cerebral hemispheres, is a slight 

 elevation pierced in the centre by a small aperture ; the 

 elevation is the infundibulum ; to it is attached in the 

 perfect state of the brain the oval, vascular pituitary 

 body {pty), which in removing the brain is almost always 

 left behind in the sella turcica (§ 48). 



486. Immediately in front of the infundibulum is a 

 strong, curved, transverse band of white fibres, giving 

 off from its convex anterior margin two strong nerves. 

 The latter are the optic nerves (//) : the transverse 

 band is constituted by the two optic tracts {o.fr), 

 which, together with the nerves, form the optic chiasma 

 {o.ch). 



487. The corpus mammillare {c.md), a rounded eleva- 

 tion immediately posterior to the infundibulum, in the angle 

 between the crura cerebri. 



488. The oculomotor nerves (third pair, ///), arising 

 one from each crus cerebri, slighdy posterior to the corpus 

 mammillare. 



489. The pathetic nerves (fourth pair, IV), arising 

 from the anterior part of the dorsal surface of the medulla 

 oblongata (valve of Vieussens, § 523), and passing outwards 

 and downwards between the cerebrum and cerebellum to 

 reach the ventral surface of the brain : their origin will be 

 best seen at a later stage. 



490. The trigeminal nerves (fifth pair, V), arising 

 from the postero-external region of the pons : each consists 

 of two roots, a large external sensory, and a small internal 

 motor root. 



491. The small abducent nerves (sixth pair, VI), 



