Houser, The Neurones of a Selachian. 95 
in this region of several important groups of neurones, They 
did see that it contains numerous bundles of nerve-fibres, how- 
ever, some of which run to the cerebellum, and so pedunculus 
cerebelli appeared to be a perfectly satisfactory designation. 
Kinespury (’97) extended the term Sfznal Vth tract to both 
the nuclei of the region and the trigeminal fibre-tract proper ; 
such use of a term originally intended to designate a definite 
group of nerve-fibres is certainly to be avoided as leading to 
confusion. JOHNSTON (’98b) appears to include a part of this 
region under his ¢uberculum acusticum. Since there appears to 
be need for a precise term which shall designate the several 
nuclei of the general cutaneous system, I therefore propose that 
the whole be called the general cutaneous nucleus. 
The general cutaneous nucleus is the continuation into the 
oblongata of the dorsal cornu of the spinal cord, and it carries 
its associated tracts with it. Its position will be seen from 
Fig. 2, g. c. x. In structure it is indeed complex, embracing, 
as it does, three groups of neurones, large numbers of nerve- 
fibres intercrossing in several directions, the spinal V tract, and 
many supporting elements. The intrinsic neurones will be con- 
sidered first. 
a. The Molecular Layer.—The molecular layer appears in 
a transverse section as a dorsal cap to the other constituents of 
the nucleus (Fig. 2, m7. 2). It is seen to be continuous with 
the cerebellar crest of the tuberculum acusticum. 
The neurones of the molecular layer are of two varieties, 
the molecular neurones and the neurones of Purkinje. Both 
of these varieties are identical with those described in Subsec- 
tion 7 for the tuberculum acusticum; their morphology will 
therefore not be given here. 
As to distribution, the minute molecular neurones are 
found scattered through the whole thickness of the molecular 
layer. The PukKINJE neurones, on the contrary, lie only in the 
deeper part of the layer, sending their great dendrites into the 
upper levels. The possible phylogenetic: significance of the 
presence of the molecular layer in this part of the brain will be 
treated in the theoretical considerations of Subsection 7. 
