732 



NOSE. 



in the opposite direction, it joins the other roots 

 to form part of tlie 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 cinerta inttrnu.) 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 covering 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 gre.it 

 part of its upper surface. It is between two and 

 a half and three lines long ; its base lies in the 

 alible 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 tract us otfactorius. 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 

 Soeinmermg, Sir C. Bell, Mr. Swan, and Valentin. 

 Weber and Hildebrandt, and Cloquet call that mid- 

 dle or yrey rtiut which lies above the others, and 

 forms a thin grey band on the uppei surface of the 

 nerve : and under the internal root they include, as 

 Haller and others did, who described only two roots, 

 both the internal 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 because their arrangement is more 

 constant than that of the grey mutter. 



or is altogether convex upon its upper surface, 

 which lies in the groove between the convolu- 

 tions. It is striated in its whole length, and 

 nearly white; though some grey 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 depth 

 in different persons, always becomes deeper 

 and more distinct. Valentin* suggests that it 

 indicates the course of the canal which in the 

 human embryo passed 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.f 



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 

 upon the dura mater covering the cribriform 

 plate ; its inner margin is in contact with that 

 covering the crista galli, and with the anterior 

 part of the fa!x cerebri ; by which alone it is 

 separated from the bulb of the opposite side. 

 It is of a greyish-red colour from the quantity 

 of grey nervous matter which is placed upon 

 its surface and among the plexuses formed by 

 the nervous filaments within it. In its interior 

 a small cavity or ventricle may be generally 

 detected by a vertical antero-posterior section : 

 it is the remains of the embryonic condition 

 just alluded to. 



From the lower surface of the bulb proceed 

 the numerous branches of the olfactory nerve. 

 They vary much in number and size both in 

 different persons, and on the tvyo sides of the 

 same individual; a want of symmetry which 

 may often be seen in the perforations of the 

 cribriform plate. The ordinary number of 

 branches is from fifteen to twenty on each side. 

 Each of them, invested by a very delicate neu- 

 rilema, passes through an aperture in the cribri- 

 form plate, through' which also a tubular pro- 

 longation of the dura mater passes and becomes 

 continuous with the periosteum of the nasal 

 fossae. The nerves, which become rather firmer 

 when they have passed through the cribriform 

 plate, ramify between the periosteum and the 

 mucous membrane, and are divisible into two 

 chief sets, some being placed upon the septum, 

 others upon the outer wall of the nose. 



The internal or septual branches are about 

 twelve in number. After passing through the 

 cribriform plate, they diverge a little as they 

 descend; the anterior going somewhat forwards, 

 the posterior backwards. The trunks soon, and 

 often while within the foramina of the cribri- 

 form plate, break up into tufts of filaments, 

 which unite into plexuses with long and narrow 

 quadrilateral meshes; and from these, smaller 



* Soemmering, Votn Baue des Menschl. Kdr- 

 pers. Bd. iv. p. '299. 



+ See on this question Cloquet's Osphresiologie, 

 and Alelzger's llistoiia. 



