460 



THE DOGFISH 



J ' 



marked difference between the brain of the dogfish and that 

 of the frog is seen in its anterior portion. In the frog, the 



diencephalon is con- 

 tinuous anteriorly 

 with the paired cere- 

 bral hemispheres ; in 

 the dogfish there is in 

 this region a relatively 

 smaller, unpaired por- 

 tion of the brain, 

 marked in front by 

 a slight groove, and 

 known as prosencep- 

 halon (VH\ which 

 represents the cere- 

 bral hemispheres of 

 the higher Verte- 

 brates but which does 

 F.rho n t become subdi- 



NH vided externally into 



paired lobes. Ante- 

 riorly it gives off, 

 right and left, a large, 

 oval olfactory lobe (L. 

 <?/) each connected 

 with the prosen- 

 cephalon by a short, 

 stout stalk (Tro) and 

 applied distally to 

 the corresponding ol- 

 factory capsule. The 



FIG. 124. Dorsal view of the brain of Scylliutn 



canicula. 



The posterior division of the brain is the medulla 

 oblongata (A r //), enclosing the fourth ventricle 

 (F. rho). The large cerebellum (HH) nearly 

 covers the optic lobes (MH ). The diencephalon 

 (ZH) shows, in the middle, the third ventricle, 

 and the place of attachment of the pineal stalk 

 (Gp). The prosencephalon (VH) gives off the 

 olfactory lobes (Tro, L.ot). The origins of 

 the following nerves are shown: optic (//), 

 trochlear (7K), trigeminal (F), facial (VII\ 

 auditory (F//7), glossopharyngeal (AY), and 

 vagus (X). (From Wiede 

 A nato my.) 



dersheim s 



prosencephalon con- 

 tains paired lateral ventricles, which communicate posteriorly 



