STRUCTURE OF THE BRAIN IN' RODENTS. 
723 
the capillary plexus beyond the striate region. These vessels in hardened preparations 
show to a marked degree the wide perivascular channels around them. The stratum 
which we above described has from its fine granular aspect been termed by Kupeeer 
stratum moleculare. It is wholly absent in Man, where, according to Meynert, the axis 
processes of the ganglionic cells unite immediately with the medulla. In the Rabbit, 
however, the spindle cell is well represented hete, not only scattered widely apart through 
the stratum moleculare, but arranged in some numbers along line of union of this 
stratum with the deeper medulla. Numbers of spindle cells of large size are also met 
with at all depths of the deep medulla of the cornu lying parallel with the direction 
of the medullated fibres. This spindle cell medulla communicates directly with the 
spindle series of the limbic lobe at the commencement of the inrolling of the cornu, 
and lies parallel throughout its course with the involutions of this organ. Occasionally 
an unusually large fusiform cell will be met with immediately beneath the ganglionic 
series measuring as much as 60gX lip, and thus rival in size the similarly large spindle 
cells met with beneath the cortex of the inner olfactory region along the course of the 
arciform fasciculi. These fusiform elements lie embedded in and continuous with the 
medulla of the fornix, and usually exhibit three or more processes, one from each pole 
of the cell following the course of the medulla and the others lateral in origin and 
smaller in diameter. One of the larger processes may often be traced directly up itito 
the layer of ganglionic cells. 
Significance ofi the Fissures and Sulci of the Brain. 
The foregoing considerations as regards the intimate structure of the cerebral 
cortex in the Rat and Rabbit, taken together with the results of my former 
examination of the cortex in the Pig, Sheep, and the Cat, lead to important 
conclusions relative to the significance of the fissures and sulci of the brain. 
Hitherto it has been customary to regard the convolutionary arrangenlent a,s 
dependent in a great measure upon the progressive growth and development of the 
cortex, restricted and modified by the encircling cranial bones, the varied folds and 
complex fissures being really in this sense mere accidents of development, their 
uniformity of distribution in different classes of animals being due to the uniform 
action of the forces thus brought into play. Out investigations would lead us to a 
far different conclusion, nor can we, judging from our histological data, regard the 
divisions mapped off from each other by fissures and primary sulci as other than 
structurally distinct organs. In no case is this so palpable as in the various regions 
of the great limbic lobe, for here both a superficial survey, i.e., of the structure of 
the cortex and an investigation of the deep medullary connexions of these regions 
conclusively confirm the statement now advanced. In the former memoir'* I insisted 
strongly upon the fact that certain sulci or fissures formed sharply-defined boundary 
* Op. cit., p. 45. 
