138 



PISCES. 



Cyclostomes alone, where it is represented by the vagus and by fibres 

 of the spinal nerves, The spinal cord, the mass of which is con 



'Fa 



FIG. 5S8. Brain and anterior part of the spinal cord and nerves of Hexanchug griseut (after 

 Gegenbaur). The nerves are dissected out on the right side ; the right eye removed. 

 A, Anterior cavity of the skull ; N, nasal capsule ; Vk, fore-brain (cerebral hemispheres) ; 

 Mh, mid-brain (optic lobes); Ce, cerebellum; Mo, medulla oblongata; Bo, olfactory- 

 bulb ; tr, trochlear nerve (fourth nerve) ; Tr 1 ', first (ophthalmic) branch of the trigeminal 

 or fifth ; a, terminal branches of the same in the ethmoid region ; Tr", second branch ; 

 Tr"', third branch; Fa, facial (seventh); Gp, glossopharyngeal (ninth); Vg, vagus 

 (tenth) ; L, lateral branch of vagus (to lateral line) ; J, intestinal branch ; Os, superior 

 oblique muscle of eye ; Hi, internal rectus muscle ; He, external rectus ; Rs, superior 

 rectus; 8, spiracle; Pg, palatoquadrate ; Hm, hyomandibular ; J2, branchial rays; 

 I VI, branchial arches ; Er, branchiae ; P, spinal nerves. 



siderably greater than that of the brain, extends tolerably uniformly 

 throughout the whole length of the neural canal, and usually does 

 not form a so-called caitda equina. Rarely its upper part presents 





