74 



- ZOOTOMY. 



23, and 25, II) : 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). 



" u 



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

 (half nat. size). 



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

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

 thalamencephalon : v. 3, third ventricle: /.*', lobus inferior: c.Ji, 

 prosencephalon. 



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

 23, 25, ///), 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). 



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



m.o, medulla oblon^ata : r, cerebellum: i.c, internal carotid artery: 

 o.l, optic lobe://, pituitary body: s.v, s.v', saccus vasculusus : ///, 

 thalamencephalon : c.h, prosencephalon : 7 A', cerebral nerves. 



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

 25, /F), delicate threads which proceed from beneath the 

 antero-lateral regions of the cerebellum, outwards and 

 forwards to their foramina in the side walls of the skull 



(i 3). 



