BRAIX. 



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. 



-Fa 



FIG. 77. Brain and anterior part of the spinal cord and nerves of Hexanchus griseus (after 

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

 removed, a terminal branches of ophthalmicus 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 ; N 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 fifth 

 nerve ; Vg tenth nerve (vagus) ; Vh cerebrum (forebrain) ; 1-6 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 



