STRUCTURE OE THE BRAIN IN RODENTS. 
721 
The vessels throughout this course exhibit wide perivascular channeling, and are 
bordered by the usual perivascular nuclei. The connective element is similar in every 
respect to that found in this layer in other parts of the brain—the larger cells, 
measuring 9/x across, are usually nearly globular, and have a nucleus 6y in diameter. 
They are very numerous, and throw off on all sides delicate fibrillar processes to 
constitute the neuroglia framework. The Dexter’s cell is found immediately beneath 
the vascular investment of the cortex. Scattered through the medullated division of 
this cortical zone, and especially near the confines of the reticular stratum, are the nerve 
cells alluded to. They are elongate spindles, measuring 34gXl2g, with an oval 
nucleus 12g in diameter. These cells lie parallel to the medullated fibres, throwing off 
branches from either pole in the direction of these fibres, but also almost invariably 
exhibiting a lateral process, which dips down into the cortex in the direction of the 
reticulated layer. These spindle cells are not numerous, and, as stated by Meynert, 
may readily be overlooked. In connexion with their presence here, it is interesting to 
recall similar spindle cells of great dimensions which have been pointed out as existing 
in certain portions of this peripheral zone in the olfactory cortex. 
Striate layer. —Immediately beneath the vascular and nervous plexus constituting 
the reticulated portion of the peripheral zone lies the striate layer, so named after the 
striated aspect given by the numerous apex processes of the ganglionic layer, which 
radiate towards their site of common union—the nerve plexus. The depth attained 
by this layer averages '558 mm., but near the commencement of the infolding of the 
true cornu ammonis it is much shallower, the branching of the apex processes occurring 
nearer to the cell. Dadiating in the same direction outwards, and lying side by side 
with these nerve processes are numerous vessels, which rise from the ependyma of the 
lateral ventricles, and after supplying the medulla of the cornu, unite with the vessels 
of the peripheral zone (from the pia mater) through the medium of its vascular plexus. 
The region of these apical radiations undoubtedly corresponds to the small pyramidal 
layer in other realms of the cortex of the Babbit. 
Ganglionic layer. —This layer is formed by cells quite characteristic in their distribu¬ 
tion of the cornu ammonis formation. It forms a shallow stratum varying in depth 
from '093g to '139g, the average depth being ‘112/r The cells vary in contour, being 
frequently oval, elongated, or fusiform, rarely pyramidal, and much more commonly of 
a swollen pegtop-like contour. At the commencement of the inrolling of the cortex to 
form the cornu the ganglionic cells may be clearly traced into this formation, first, as 
a scattered series or deep belt, in which the cells approximate closer and closer until they 
form a belt two to five deep, in which the cells are so closely applied to each other as to 
be in actual contact, and form an almost unbroken file through the greater portion of the 
true cornu ammonis ; beyond the second turn of this sigmoid fold, however, they again 
become more widely separated and scattered so as to form a deeper belt. In hardened 
sections the shrinking separates the cells widely apart, and they may be observed sur¬ 
rounded by a clearly defined pericellular space. In fresh sections, on the other hand, 
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