116 



far back bene=ith the diilbrain; consult Pii?.l. Its large size 

 is merely the expression of the unusual importance which is 

 assumed by this part of the interbrain in selachians. Intrin- 

 sic neurones, ani fibres from vrithout ara to be noted in num- 

 bers in both the infmdibulum and the lobi inferiores. 



The wall of the infundibulum exhibits neurones separated 

 from each other by considerable intervals {Bi^.2^.). The cell- 

 body is polygonal or elongated-ov^l in form. The dendrites 

 are tei in number. They spread ^videly, rarely branch, and 

 pursue a nearly straight course. 



Tfie Lobi I^zferiores are the most conspicuous feat ires of 

 the hypothalamus, a pair of great bulbous outpushings of the 

 lateral wall of the infundibalum (?'ig.l, l.i.). These lobes 

 are the seat of a crowded group of neurones, a fact which is 

 doubtless the ontogenetic cause of their large size. 



Herrick ( '92) has described several distinct nuclei from 

 the lobus inferior (hypoarium) of the teleost, but I have found 

 it impracticable to distinguish cell-groups in Mustelus. The 

 neurones are disposed in a layer next to the limitans interna, 

 the cell-bodies forming a closely-packed zone involving some- 

 thing like the inner fourth of the thickness of the wall (Pig. 

 27, i.z. ). The dendrites are directed outward, forming, to- 

 gether with the nerve-fibres here, a fine tangle which presents 

 the appearance of a molecular layer with general stains. 



The form of a neurone is quite unlike that of any other 



