Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/945

Rh NOSE,] A N A T O M Y 885 outer margin to the free edge of the nasal bone and supe rior maxilla, whilst by its inner it is continuous with the anterior border of the septal cartilage. The lower lateral cartilage curves inwards upon itself, touches its fellow in the mesial plane at the tip, and forms the anterior and lateral boundary of the orifice of the nostril. It is con nected by fibrous membrane above to the upper lateral cartilage, and behind to the anterior edge of the superior maxilla. In this membrane two to five small cartilaginous plates, called the epactal cartilages, are often found imbedded. The skin of the nose which covers the lower lateral cartilages contains numerous sebaceous follicles, which open by comparatively large orifices on the surface. It is closely connected to these cartilages, and to the muscles of the alae. The lower lateral cartilage forms the wall of the vestibule or entrance to the nasal chamber, and the vestibule is lined by a prolongation of the integument, which 13 studded with numerous short hairs or vibrissce. Each nasal chamber is lined by a mucous membrane called the pituitary or Schneiderian. This membrane is prolonged into the meatuses and the air sinuses which open into them; posteriorly it is continuous with the mucous lining of the pharynx, and anteriorly it blends with the cutaneous lining of the vestibule. The pituitary membrane is thick and soft, and diminishes the size of the meatuses and the openings of the air sinuses as seen in the skeleton. The mucous membrane is divided into a respiratory and an olfactory region. The respiratory region corresponds to the floor of the nose, to the inferior turbinated bone, and to the lower third of the nasal septum. It is covered by a ciliated columnar epithelium, and contains numerous race mose glands for the secretion of mucus or pituita. It is also vascular, and the veins which ramify in it have a plexiform arrangement. The mucous lining of the air sinuses is also ciliated, but almost devoid of glands, except in the antrum, in which region the glands sometimes dilate into cystic tumours. The olfactory region is the seat of distribution of the olfactory nerve and of its peripheral end-organs. It corre sponds to the roof of the nose, to the superior and middle turbinals, and the upper |rds of the septum. The mucous membrane is thick, soft, easily destroyed, of a yellowish brown colour, and blended with the periosteum. &quot;When vertical sections through this membrane are examined microscopically the tubular glands discovered by Bowman may be seen in its vascular con nective tissue layer. These glands contain roundish secreting cells with yellowish-brown pigment-stained contents. The epithelium is cylindrical, but not usually ciliated, though patches of ciliated epithelium cells are said to occur in man. Long, slender, and even branched processes proceed from the deeper end of each cell towards or even into the sub- epithelial connective tissue. The colls usually contain pigment granules. Between the epithe lium cells the characteristic olfactory cells of Schultze are situated. Each olfactory cell con sists of a globular or fusiform body, from which olfactory two long processes arise : one, the peripheral {j^* c ^{_ process, passes vertically between the adjacent thtiiuin cell ; cylindrical epithelium cells to the free surface ^.u. citTpTi- of the mucous membrane: in amphibia, rep- J- heral ; **&p, t-i j,. , ., ., , , , * its central T- tiles, and birds it projects beyond the plane ncose process, of the epithelium as a simple hair-like struc- ufla &quot; &hultu -&amp;gt; ture, or subdivided into several slender &quot;olfactory hairs;&quot; in fish and mammals, man inclusive, it ends, without form ing a hair-like prolongation, on the general plane of the mucous surface. The second or central process of the olfac- tory cell extends towards the sub-epithelial connective tissue : it is finer than the peripheral process, and has not unfrequently a varicose appearance like a nerve fibre. In the description of the development of the brain (p. 8C i), the origin of the olfactory bulb and peduncle from the hemisphere vehicle was referred to. In the adult brain the olfactory peduncle is in contact with the under surface of the frontal lobe. It is a white band, which divides in front of the locus perforatus anticus into three so-called roots of the olfactory nerve. The external or long root passes outwards across the Sylvian fissure to the gyrua hippocampi, and perhaps also to the insula : a few fibres are continuous with the anterior commissure; but in mammals, where the olfactory peduncle forms a good- eized lobe, it receives many fibres from the commissure. The middle or yrey root contains white fibres which proceed from the corpus striatum. The internal or short root has been traced into the anterior end of the gyrus fornicatus; hence the inner and outer roots of the olfactory peduncle are connected with the anterior and posterior extremities of the arch-shaped gyrus. The olfactory bulls rest on the upper surface of the cribri form plate of the ethmoid, one on each side of the crlsta galli. The bulb consists both of grey and white matter, and sometimes retains the central cavity lined by a ciliated epithelium. The grey matter contains fusi form and pyramidal nerve cells imbedded in neuroglia (the stratum gelatinosum of L. Clarke). Between it and the central cavity Ls the white matter formed of nerve fibres interspersed with &quot; granules,&quot; similar to those seen ill the rust coloured layer of the cerebellum. Between the grey matter and the surface is the stratum glomerulosum of Meynert, which apparently consists of coils of the olfactory nerve fibres with interspersed &quot;granules.&quot; The olfactory nerve fibres form the first pair of cranial nerves or nerves oi smell; they leave these glomeruli in from 15 to 25 bundles, and enter the roof of the nose through the holes in the cribri form plate (PI. XIX. figs. 1, 2); they lie in grooves in the bones of the olfactory region, and form a network from which bundles of fine non-medullated fibres arise that enter the mucous membrane and run between the glands into the epithelial layer. These nerves have a varicose appearance, and though their terminations have not been precisely ascertained, it is believed that they are connected with the central processes of the olfactory cells, which cells are therefore regarded as the peripheral end-organs of the olfactory nerve fibres. The mucous membrane of the nose also receives branches from the 1st and 2d divisions of the 5th cranial nerve. Their mode of termination in that membrane is not known, but they are associated with the sense of touch, and not with the special sense of smell. i i The EVEBALL, globe of the eye, or organ of vision, is a EyelaU, complex optical apparatus situated in the cavity of the orbit, imbedded to a large extent in loose fat, and with several muscles attached to it. Its form approximates to the spheroidal, but it actually consists of segments of two spheres, the posterior of which is the larger. The eyeball consists of three coats or tunics, which enclose three translucent refracting media. The first or external coat consists of a posterior, white, opaque part, the sclerotic, which corresponds in its area with the posterior larger segment of the ball, and of an anterior, translucent part, the cornea, which corresponds in its area with the anterior smaller segment of the eyeball Piercing the sclerotic coat is the optic nerve, which enters the globe about -|th inch to the nasal or inner side of its antero- posterior axis. The second or middle coat, or tunica vasculosa, consists of a posterior part or choroid, the area of which corresponds almost exactly with the sclerotic;