150 



ZOOLOGY 



~SECT. 



(lat. vag^ which runs along beneath the lateral line to the posterior 

 end of the body. The rest of the nerve runs backwards to divide 

 into cardiac branches for the heart and gastric branches for the 

 stomach. 



The spinal cord is a cylindrical cord which extends from the 

 foramen magnum, where it is continuous with the hind brain, 

 backwards throughout the length of the neural canal enclosed by 



JX 5 ^ 



tcc.V t/V^ 



V* 



sp.c 



FIG. 777. Scyllium catulns. 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 are dotted. The ophthalmicus prof undus and the buccal branch of the facial 

 are not represented ; cl.\ d.^, branchial clefts ; ep. epiphysis ; ext. rect. external rectus 

 muscle of the eye-ball ; gl. ph. glossopharyngeal ; hor. can. horizontal semicircular canal ; 

 hy. mnd. VII. ', hyomandibular portion of the facial ; inf. old. inferior oblique muscle ; int. 

 rect. internal rectus muscle ; lat. Tag. lateral branch of vagus ; mx. V. maxillary division of 

 the trigeminal ; olf. cps. olfactory capsule ; off. s. olfactory sac ; oph. 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 ; *. olb. superior 

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



the neural arches of the vertebrae. As in the Craniata in general 

 (see p. 92), it has dorsal and ventral longitudinal fissures and 

 a narrow central canal, and gives origin to a large number of 

 paired spinal nerves, each arising from it by two roots. 



Organs of Special Sense. The olfactory organs are rounded 

 chambers enclosed by the cartilage of the olfactory capsules of the 

 skull, and opening on the exterior by the external nares on the 

 ventral surface of the head. The interior has its lining membrane 

 raised up into a number of close-set ridges running out from 



