732 
in the opposite direction, it joins the other roots 
to form part of the pyramid. 
The middle root* arises between the two 
preceding roots, and first appears in two or 
three bands of fibres just in front of the sub- 
Stantia perforata antica, whence they proceed 
forwards to join the other roots. 
Each of these roots is connected with grey 
matter prolonged from the surface of the ante- 
rior lobe and the fissura Sylvii, and especially 
from two slight elevations, one of which lies in 
the concavity of the internal, the other in that 
of the external, root, as they severally turn for- 
wards where they join the middle root. The 
grey matter connected with the external root 
covers part of its origin, is continued along 
both its sides, and conceals more or less the 
filaments which join its outer border. Then 
connecting itself with the grey matter around 
the fibres of the middle root, they pass forwards 
together, and are lost near the apex of the pyra- 
mid ; part of them entering its substance, but 
a greater portion forming a thin layer (propago 
cinerea externa) which covers its surfaces, 
especially the upper one. The grey matter 
connected with the inner root conceals many of 
the fasciculi of its origin, and two streaks pro- 
ceed from it, of which one passes into the inte- 
rior of the pyramid, separating the internal and 
middle roots, and the other, of much larger 
size, is continued over its surface. This latter 
is the middle or grey root of Cloquet, &c. (the 
propago cinerea interna.) It has a somewhat 
pyramidal form, and covers a part of both sur- 
faces of the pyramid, but chiefly the upper 
surface. Its deepest edge penetrates to the 
middle root, and its outer edge sometimes 
joins the superficial layer covermg the other 
roots. As it proceeds forwards it becomes 
more and more slender; and it is prolonged 
further on the upper than on the lower surface 
of the pyramid, near the apex of which it ceases. 
Thus, the pyramid of the olfactory nerve is 
formed by three fasciculi of white filaments, 
separated by streaks of grey matter, by which also 
it is covered on both its borders and on a great 
part of its upper surface. It is between two and 
a half and three lines long ; its base lies in the 
angle where the two internal convolutions of the 
anterior_lobe diverge; and at its anterior extre- 
mity, becoming gradually smaller and flatter, it 
is continued into that which may be called the 
trunk of the nerve, the éractus olfactorius. This 
is nearly flat: it is grooved along the middle of 
its under surface, which rests on the upper part of 
the body of the sphenoid bone, and has a ridge, 
* Confusion has arisen in the use of this name. 
The root here meant is that called middle root by 
Soemmering, Sir C. Bell, Mr, Swan, and Valentin. 
Weber and Hildebrandt, and Cloquet call that mid- 
dle or grey root which lies above the others, and 
forms a thin grey band on the upper surface of the 
nerve: and under the internal root they include, as 
Haller and others did, who described only two roots, 
both the intefnal and middle ones. The names 
. here adopted are preferable, because the white 
fasciculi alone could properly be regarded as roots 
of a nerve, they alone being continued to the 
branches, and becanse their arrangement is more 
constant than that of the grey matter. 
‘ 
NOSE. 
or is altogether convex upon its u surface, 
which lies in the cropee' betereee thay enone 4 
tions. It is striated in its whole length, and — 
nearly white; though some matter is col- 
lected within the meshes of the plexuses, which _ 
its fibres form as they proceed forwards and a — 
little inwards towards the bulb in which they 
expand. After long immersion in spirit, the 
groove on the under surface of the trunk, 
which, in the recent state, varies much in 
in different persons, always becomes deeper 
and more distinct. Valentin* suggests 
indicates the course of the canal which in the 
human embryo from the lateral ventricle 
to the end of the olfactory bulb. The analogue — 
of this canal is persistent in the olfactory nerves 
of lower Mammalia; but there is no sufficient - 
evidence of its having been ever seen in the 
human adult; at least in this part of the 
nerve.t a 
The bulb of the olfactory nerve is a nearly — 
elliptical flat body, about half an inch long, 
slightly furrowed above, convex on its lower 
surface, and evenly rounded in front. It rests” 
be the dnra mater covering the cribriform 
plate; its inner margin is in contact with that 
covering the crista galli, and with the anterior 
part ts falx cerebri; by which alone it is 
separated from the bulb of the onperes ide 
It is of a greyish-red colour from the quantity 
of grey nervous matter which is placed upoi 
its surface and among the plexuses formed b 
the nervous filaments within it. In its in 
a small cavity or ventricle may be ge 
detected by a vertical antero-posterior section 
it is the remains of the embryonic conditio1 
just alluded to. a 
From the lower surface of the bulb procees 
the numerous branches of the olfactory nerve 
They vary much in number and size both | 
different persons, and on the two sides of th 
same individual; a want of symmetry whic 
may often be seen in the perforations of 
cribriform plate. The ordinary number o 
branches is from fifteen to twenty on each sidi 
Each of them, invested by a very delicate ne 
rilema, passes through an aperture in the erik 
form plate, through which also a tubular 5 
longation of the dura mater passes and becot 
continuous with the periosteum of the ni 
fosse. The nerves, which become rather fin 
when they have passed through the cribri 
plate, ramify between the periosteum and 
mucous membrane, and are divisible into ~ 
chief sets, some being placed apon the sept 
others upon the outer wall of the nose. 
The internal or septual branches are a 
twelve in number. After passing through 
cribriform plate, they diverge a little as 
descend; the anterior going somewhat forw 
the posterior backwards. The trunks soon 
often while within the foramina of the | 
form plate, break up into tufts of filar 
which unite into plexuses with long and na 
quadrilateral meshes; and from these, sn 
* Soemmering, Vom Baue des Menschl. | 
pers. Bd. iv. p. 2 a 
+ See on this question Cloquet’s Osphres 
and Metzger’s Historia, 
