THE BRAIN. 



139 



In the Angler (Lophius piscatorius, a Teleostean) there is also a superficial 

 layer of enormous nerve-cells (about 200 in number) behind the calamus scrip- 

 torius of the sinus rhomboidalis, filling up the dorsal fissure of the spinal cord for 

 a certain distance : their discoverer, G. Fritsch, calls them " lobi nervi lateralis." 

 The axis fibres arising from these cells accompany the trigeminal and vagus, 

 but do not go to electric organs, which are entirely wanting in Lophius, but to 

 the integumentary sense-organs, which are enormously developed in this Fish, 

 and also to the "lure. :> The similarity in position of these nerve centres 

 to the electric lobes of Torpedo, however, deserves notice. 



FIG. 112. BRAIX OF Myliobatis aquila, in situ. (From the ventral side. ) 

 (After Eohon.) 



7, olfactory, II, optic, 777, oculomotor, IV, trochlear, V, trigeminal, VI, abducent, 

 VII, facial, J'777, auditory, IX, glossopharyngeal, and X, vagus nerves ; VH, 

 prosencephalon ; H, HS, hypophysis and infiindibulum ; UL, lobi inferiores ; 

 Sv, saccus vasculosus ; Ctr, transverse commissure ; Geh, auditory capsule ; Jf ", 

 vertebral column ; R, spinal cord. 



Teleostei. The type of brain found in Teleosteans is also 

 specialised, and restricted to the members of this order. 



As is the case in nearly all Fishes, the brain by no means fills 

 the cranial cavity, as already mentioned in the description of the 

 brain-membranes, and as a rule it is separated from the roof of the 

 skull by a greater or less amount of a lymph-like fluid. 



The form of the brain in Teleostei varies greatly, more by far 

 than in any other Vertebrate group. It is therefore difficult to 

 give a general description of it, and only the following essential 

 points can be mentioned here. 



It never attaios to so large a relative size as does that of Elas- 

 mobranchs. The peripheral region, as already mentioned (p. 137), 



