734 
MR. W. BEVAH LEWIS OR THE COMPARATIVE 
sulcus. This passage of the inner marginal fibres of the band into the cortical sub¬ 
strata must eventually lead to its total disappearance. These fan-like radiations are 
continuous with the cells of the cortical layers ; yet it does appear as though a con¬ 
nexion was also established betwixt its innermost fibres and the claustrum, which 
latter formation, however, is mainly continuous with the arciform spindle-celled medulla 
of the olfactory area (Plate 49, fig. 8, d). Prior to the arrival of this superficial 
medullated band at the Sylvian furrow a notable diminution in its width has occurred, 
apparent to the naked eye. This is due to the detachment from its margin of a large 
proportion of fibres which have already been alluded to as running continuous with 
the deep olfactory medulla within the olfactory area. It has been usual to speak of 
the central projections of the olfactory medulla under the terms olfactory roots, an 
external, middle, and internal root being usually those described in higher animals. 
A fourth also is described as a superior root, connecting the upper surface of the 
olfactory lobe to the hemisphere. By the external root is indicated what I have above 
described as the superficial olfactory fasciculus; the connecting system with the striate 
body is identical with the so-called middle root, whilst the arciform series includes the 
remaining two roots, the internal and superior. 
Dissection of Based Olfactory Regions. 
The tracing of the coarser strands of medullated fibres by microscopic examination 
of sections, should invariably be supplemented, where possible, by frequent dissections 
which often enable us to fully confirm by this second method results arrived at by the 
former. As regards the olfactory regions at the base the following points may by this 
method be satisfactorily demonstrated in the Babbit and the Bat:— 
a. Uninterrupted course of the central olfactory fasciculus into anterior com¬ 
missure. 
b. Projection of posterior olfactory fasciculus into tlie occipital lobe. 
c. Connexion of the latter fasciculus also with the cortex of the vertex. 
d. Peculiar connexion of the same fasciculus with the corpus striatum. 
e. Belationships of olfactory area at greatest depth below cortex. 
f Descent of the taenia semicircularis into olfactory area. 
The above facts may be confirmed by placing the brain of the Bat in its natural 
position with the vertex upwards, and keeping it during dissection moistened occa¬ 
sionally by a few drops of a Sf per cent, solution of common salt. With a delicate 
pair of dissecting scissors the membranes stretching across between the hemispheres are 
divided through their whole length, and the latter sliced otf horizontally outwards 
upon a level with the corpus callosum by a sharp and fine scalpel. This commissure is 
next divided along the median line from behind forwards, each segment being turned 
outwards. Such a section exposes the corpus striatum in its extra- and intra- 
