142 JOURNAL OF ComPARATIVE NEUROLOGY. 
3. Hypothalamus: The Lobi Inferiores. 
The hypothalamus is very large in Mustelus, projecting 
far back beneath the midbrain; consult Fig. 1. Its large size 
is merely the expression of the unusual importance which is 
assumed by this part of the interbrain in selachians. Intrinsic 
neurones, and fibres from without are to be noted in numbers 
in both the infundibulum and the lobi inferiores. 
The wall of the infundibulum exhibits neurones separated 
from each other by considerable intervals (Fig. 26). The cell- 
body is polygonal or elongated-oval in form. The dendrites are 
few in number. They spread widely, rarely branch, and pursue 
a nearly straight course. 
The Lobi Inferiores are the most conspicuous features of 
the hypothalamus, a pair of great bulbous outpushings of the 
lateral wall of the infundibulum (Fig. 1, Z z.). These lobes are. 
the seat of a crowded group of neurones, a fact which is doubt- 
less 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 (Fig. 
27,2. 2.). 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 
found in the anterior divisions of the brain. It is not dissimilar 
to a widely spreading bush, the cell-body being the short stem, 
and the dendrites the top (Fig. 28). The dendrites are thick 
at their bases, they give origin to only a few branches, they 
taper gradually, and their tips usually reach almost to the lim- 
itans externa. The surface of a dendrite exhibits a multitude 
of spiny gemmules of various sizes. 
The course taken by the axone depends upon the position 
of the neurone. A neurone lying in the roof gives off its axone 
