BRAIN. 



133 



no pineal eye (parietal organ). The pituitary body lies along 

 the ventral side of the infundibulum ; it is said to open in the 

 adult into the cranial cavity within the dura mater (Haller), 

 but this must be regarded as doubtful. 



Fig. 77. — Brainjand anterior part of the spinal oord and nerves of Hexanchus griseus (after 

 Gegenbaur, from Claus). Tlie nerves are exposed on tlie right side, and the right eye is 

 removed, a terminal brandies of oplithalmicus superficialis trigemini ; Bo olfactory lobe ; 

 Br branchiae ; Ce cerebellum ; Fa seventh nerve (facial) ; Hm hyomandibular ; Gp ninth 

 nerve (glossopharyngeal) ; J intestinal branch of vagus ; L lateralis of vagus nerve ; Mh 

 optic lobes (mid brain) ; Mo medulla oblongata; .A'^ nasal capsule; Os superior oblique 

 muscle of eye ; P spinal nerves ; Pq palatoquadrate ; R branchial rays ; Re external, Ri 

 internal, Rs superior rectus muscle of eye ; S spiracle ; tr fourth nerve (trochlear) ; Tr' 

 ophthalmicus superficialis trigemini ; Tr" superior, Tr'" inferior maxillary branch of the fiftli 

 nerve ; Vg tenth nerve (vagus) ; Vh cerebrum (forebrain) ; l-H branchial arches. 



The cerebrum is generally marked by longitudinal grooves 

 indicating the internal division, but in Carcharias (Fig. 78), 

 Sphyrna, etc., there are no traces of these. Plagiostomes 



