CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
743 
the middle layer which consists of glomeruli olfactorii. These occupy all the anterior 
side of the mass of small cells, and extend a short distance both above and below 
along the sides ; the posterior contour of this middle layer is not however regular, 
but is rather concavo-convex in outline. 
The glomeruli olfactorii (fig. 23) were first discovered by Leydig.* He gives a 
figure which differs considerably from mine, and shows only granular neuroglia and no 
fibrillm; at one end is a compact bundle of unseparated fibres going to the olfactory 
organ, at the other end a group of uncleated cells attached to the glomerulus by 
fibrils. The difference in the mode of treatment usual at that time would account 
probably for the non-separation of the fibrillar network. 
The anterior layer consists of interlacing bundles of fibres passing from the anterior 
end of the glomeruli in a more or less curved course to the connective tissue frame¬ 
work which supports the follicles of the olfactory organ. 
The most conspicuous difference to be observed in this lobe, as compared with the 
corresponding part in the Teleostei, is the much higher development of the glomeruli, 
which in the osseous fishes are represented by merely an undifferentiated mass of 
neuroglia. 
The peduncle has also three layers. The interior is occupied by a layer of small cells 
which surround the lumen of the peduncular passage. Outside these is a stratum of 
glomeruli which extends round the internal layer on all sides, except one very small 
gap. They are placed thicker at the anterior end of the peduncle, and gradually thin 
out on approaching the cerebrum; they cease entirely within one section from that 
body. The outer circumference of the peduncle is occupied by the fibres derived from 
these glomeruli, which also become more numerous, and occupy a larger space on 
proceeding more forward. 
The description above given is taken from specimens of Scyllium ; in the other 
species examined essentially the same disposition of the layers is found. 
We now go more particularly into the minute structure (fig. 23), commencing with 
the third or internal layer. This layer is composed of a granular neuroglia, in which 
ramify fibrillae of extreme tenuity forming an extensive network. In this are 
embedded numerous small cells ; these are oval, pear-shaped, or spherical, and in many 
cases show a nucleus and nucleolus ; they give off processes which join the net¬ 
work. In Scyllium and Acanthias they are of about the same size. The larger ones 
measure about 9p, long by 7//, broad; from these to the smaller ones of 5/x, there is 
every variety of dimensions. In the Rays also they are of about this size. In Rhina 
are a trifle larger, varying from 13p, by 8/r to 8/x in diameter. Cells of these 
different sizes are seen scattered thickly throughout the layer. 
The glomeruli (fig. 23) are elongated pear-shaped or oval masses arranged generally 
with their long axes in the direction of the nerve fibres ; that is to say, one end is 
turned toward the internal and the other toward the first or external layer. They 
* ‘ Beitrage z. Mikr. Anatomie u. Entwickelungsgeschichte d. Rochen u. Haie,’ Leipzig, 1852. 
