74 



ZOOTOMY. 



23, and 25, //) : 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). 



C£. JJLO. 



Fig. 24. — Raja batis. Longitudinal vertical section of the brain 

 (half nat. s,ize). 



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

 c.i: crus cerebri: o.l, optic lobe; aq.s, aqueduct of Sylvius: th, 

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

 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 httle behind the lobi infe- 

 riores, and passing outwards and forwards to their foramina 

 in the side walls of the skull (§ 30). 



0.1 ^'^f 



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



m.o, medulla oblongata: rf, cerebellum: i.c, internal carotid artery : 

 o.l, optic lobe://, pituitary body: sv, s.-J, saccns vasculosus : th, 

 thalamencephalon : c.h, prosencephalon : / — X, 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 

 forwards to their foramina in the side walls of the skull 

 (§ 30)- 



