74 



ZOOTOMY. 



23, and 25, 77) : their proximal ends are fused together to 

 form an optic chiasma (Fig. 23, o.c). Each nerve 

 passes outwards and forwards to the corresponding optic 

 foramen ( 30). 



.4 



FIG. 24. Raja batis. Longitudinal vertical section of the brain 



(half nat. size). 



m.o, medulla oblongata : z>. 4, fourth ventricle : cb, cerebellum : 

 c.c, cms cerebri : o.l, optic lobe: aq.s, aqueduct of Sylvius: ///, 

 thalamencephalon : v. 3, third ventricle: l.i, lobus inferior: c./i, 

 prosencephalon. 



184. The third pair of nerves (oculomotores, Figs 22, 

 23, 25, 777), arising one on either side of the base of the 

 brain from the crura cerebri, a little behind the lobi infe- 

 riores, and passing outwards and forwards to their foramina 

 in the side walls of the skull ( 30). 



civ 



E m.0 



FIG. 25. Raja batis. Side view of the brain (half nat. size). 



m.f>, medulla oblongata : cb, cerebellum: i.c, internal carotid artery: 

 o.l, optic lobe://, pituitary body: s v, s.v', saccns vasculosus : th, 

 thalamencephalon: c./i, prosencephalon: IX, cerebral nerves. 



185. The fourth pair of nerves (pathetici, Figs. 22, 23, 

 25, IV), delicate threads which proceed from beneath the 

 antero-lateral regions of the cerebellum, outwards and 

 fonvards to their foramina in the side walls of the skull 



(* 30). 



