160 



ZOOLOGY 



SECT. 



two olfactory lobes two small nerves, the terminal or pre- 

 olfactory, arise from the prosencephalon : they are the nerves of 

 ordinary sensation for the interior of the olfactory sacs. From the 

 optic chiasma the two optic nerves (Figs. 821, 823, 823 bis, II) 

 run outwards through the optic foramina into the orbits, each 

 perforating the sclerotic of the corresponding eye and terminating 

 in the retina. The third, fourth, and sixth pairs of nerves have the 



sp.co 



FIG. 823. Scyllium catulus. Dissection of the brain and spinal nerves from the dorsal 

 surface. The right eye has been removed. The cut surfaces of the cartilaginous skull and 

 spinal column arc dotted. The buccal branch of the facial is not represented ; 

 d,\d.^ branchial clefts ; ep. epiphysis ; ex. rect. external rectus muscle of the eye- 

 ball ; gl. ph. glossopharyngeal ; hor. can. horizontal semicircular canal ; hy. mnd. V If. 

 hyomandibular portion of the facial ; inf. old. inferior oblique muscle ; int. rect. internal 

 rectus muscle ; lat. vag. lateral branch of vagus ; mx. V. maxillary division of the 

 trigeminal ; olf. cps. olfactory capsule ; olf. s. olfactory sac ; op/t. V. VII. superficial 

 ophthalmic branches of trigeminal and facial ; path, fourth nerve ; pi. VII. palatine branch of 

 facial ; sp. co. spinal cord ; spir. spiracle ; s. rect. superior rectus muscle ; s. olb. superior 

 oblique ; vag. vagus ; vest, vestibule. (From Marshall and Hurst.) 



general origin and distribution which has already been described 

 as universal in the Craniata (p. 104). 



The trigeminal (Figs. 821,823, 823 bis, V) arises in close relation 

 to the facial. As it passes into the orbit it swells into a ganglion 

 the Gasserian. Its chief branches are three in number. The 

 first given -off is the superficial ophthalmic (Fig. 823, oph. V\ 

 Fig. 823, bis, V op.), which runs forwards through the orbit above 

 the origin of the recti muscles, and in very close relation with the 

 ophthalmic branch of the facial. Anteriorly it breaks up into 

 branches distributed to the integument of the dorsal surface of 



