and criste the capillary networks are numerous and finely meshed, but in the remaining portions of the utriculus, sacculus, and semicircular canals, they form coarser networks. The cochlear branch accompanies the divisions of the auditory nerve as far as the first spiral turn of the cochlea; the arteries supplying the remaining turns enter the axis of the modiolus, where they divide into numerous branches. The latter are coiled in a peculiar manner, forming the so-called glomeruli arteriosi cochlea. From these, branches are given off which penetrate the vestibular wall of the lamina spiralis ossea, where they supply the limbus spiralis and the small quantity of connective tissue in the membrana vestibularis. Other branches surround the scala vestibuli, supply the walls of the latter, and then continue to the ligamentum spirale, the stria vascularis, and the lamina basilaris.

Fig. 351.-Scheme of distribution of blood-vessels in labyrinth (after Eichler): g, Artery; h, spiral ganglion; i, vein; v, scala vestibuli; Dc, ductus cochlearis; c, capillaries in the ligamentum spirale; d, capillaries in the limbus spiralis; f, scala tympani.

The venous trunks lie close to the arteries and receive their blood from the veins which lie at the tympanal surface of the lamina spiralis and from those which encircle the outer wall of the scala tympani. The former, in turn, receive their blood from the capillaries of the limbus spiralis; the latter, principally from the region of the ligamentum spirale and the basilar membrane.

From this description it is seen that the arterial channels are connected with the scala vestibuli, the venous with the scala tympani, and that the inner blood stream circulating through the lamina spiralis and limbus spiralis is separated from the blood current of the two scale, the ligamentum spirale, and the crista basilaris (Eichler).

The entire membranous labyrinth is filled with endolymph. The ductus endolymphaticus is, as will be remembered, a canal ending

under the dura in a saccus endolymphaticus. In connection with the latter are epithelial tubules bordering upon lymph-channels, with which they probably communicate by means of interepithelial (intercellular) spaces (Rüdinger, 88). The efferent channels for the perilymph of the vestibule extend along the nerve sheaths of those nerves supplying the maculæ and crista; these passageways finally communicate with the subdural or subarachnoid spaces. The perilymph of the cochlea is carried off by the adventitious tissue of the vena aqueductus cochleæ, the lymph-vessels of which empty into certain subperiosteal lymph-channels near the inner margin of the jugular fossa.

4. ON THE DEVELOPMENT OF THE LABYRINTH.

In man the epithelium lining the membranous labyrinth originates from the ectoderm as a single-layered epithelial vesicle, the auditory vesicle or the otocyst, during the fourth week of embryonic life. After being constricted off from the ectoderm, this vesicle lies in the vicinity of the epencephalon and is surrounded by mesenchyme. The auditory vesicle then develops a dorsomesial evagination, which gradually grows larger and finally becomes the ductus endolymphaticus. An evagination also occurs in the ventral wall of the vesicle, the recessus cochleæ. At the same time the mesial wall is pushed inward, thus incompletely dividing the vesicle into two smaller sacs-the dorsal utriculus and the ventral sacculus. From the utricular portion there arises a horizontal evagination, flat and quite broad-the first trace of the lateral or horizontal semicircular canal; soon after, another evagination, vertical and still broader than the first, is seen-the anlage of the other two canals. The outer portion of these pouches gradually expands, while in the middle, the two layers of each evagination come in contact with each other and coalesce, finally becoming absorbed. In the vertical evagination two such areas of adherence are found, thus forming a superior and a posterior canal, both having a common crus at one end.

The recessus cochleæ grows both in a longitudinal and in a spiral direction, forming the cochlear duct.

In the immediate vicinity of the membranous labyrinth, the mesenchyme is differentiated into a connective-tissue wall for the former. The successive layers of mesenchyme, except in those areas where the membranous labyrinth later becomes adherent to the osseous, are transformed into a mucous connective tissue. The latter is surrounded by a more compact tissue, from which are derived, first, cartilage; then bone and periosteum, and thus, finally, the osseous labyrinth. By a peculiar process of regressive metamorphosis most of the mucous connective tissue later disappears. In the adult it is replaced by the perilymphatic spaces of the labyrinth (compare Retzius, 84; Schwalbe, 87).

TECHNIC.

329. In the treatment of the external and middle ear the usual methods are employed. For the study of the epithelium in conjunction with the adjacent bone the tissue is fixed and then decalcified, or subjected to those fixing methods which accomplish both processes at the same time. The latter method, however, can be applied only to very small objects.

330. The manipulation of the membranous labyrinth, especially that of the adult, is a very difficult technical problem. Its isolation from the petrous portion of the temporal bone without injury can be accomplished only in well-advanced fetuses and in children, and even here a thorough knowledge of the situation of the parts in the petrous portion of the temporal bone is essential. Smaller animals, especially rodents, afford better specimens. In the latter, the semicircular canals and cochlea give rise to more or less distinct projections into the tympanic cavity. If the latter be opened, the situation of the parts may be ascertained from without. In the rabbit and guinea-pig, the entire cochlea projects into the tympanic cavity, and may be easily removed in toto with a strong knife, and, as the bony cochlea in these animals has very thin walls, it offers very little resistance to the decalcifying fluid (use, for instance, 3% nitric acid).

331. According to Ranvier's method (89), the cochlea is opened with a scalpel in a 2% solution of osmic acid in normal salt solution. After twelve hours the cochlea is placed for decalcification in 2% chromic acid, which is frequently changed. In guinea-pigs, for instance, decalcification is accomplished in a week.

332. According to the method of Retzius (84), the opened cochlea is treated for half an hour with a 0.5% aqueous solution of osmic acid, and then for the same length of time with a 0.5% aqueous solution of gold chlorid. The organ of Corti is then dissected out and examined as a whole, or cut after carefully removing the bone.

333. The labyrinth of the human adult is usually prepared as follows: The apex of the petrous portion of the temporal bone is removed and the upper semicircular canal, together with the cochlea, opened in Müller's fluid; in this solution the pyramid is left for three weeks; during the first week the fluid is changed daily, and every two days during the following weeks. The specimen is then washed for twenty-four hours in running water, placed in 80% alcohol for two weeks, and finally in 96% alcohol for two days. The preparation is now ready for decalcification. This is done with 5% nitric acid, which is to be changed daily (ten days to two weeks). Then follows washing for two days in running water, carrying over into 80% alcohol for twenty-four hours, then into 96% alcohol for from six to eight days, and, finally, infiltration and imbedding in celloidin (A. Scheibe).

334. The following method may also be employed with good results: The isolated pyramid with opened semicircular canal and cochlea is treated with Müller's fluid for two days at room-temperature, and then for three weeks in a thermostat at 23° C. During the latter period, the fluid should be changed. The specimen is then washed for forty-eight hours in running water, treated for fourteen days with 80% alcohol, then for eight days with 96% alcohol, decalcified, and further treated as in the preceding method.

335. Up to the present time it has been customary to cut sections in celloidin; but the combined celloidin-paraffin method may also be employed with good results, and even the paraffin method, if great care be exercised in imbedding the tissue.

336. The nerve-fibers and nerve-endings of the cochlea may be stained with the chrome-silver method. For this purpose it is recommended to employ embryos or young fetuses.

X. THE ORGAN OF SMELL.

THE nasal cavity consists of the vestibule, the respiratory region with the accessory cavities, and the olfactory region.

The vestibule is lined by stratified squamous epithelium. In the region of the anterior nares are hairs, the sebaceous glands of which are markedly developed, while at the level of the cartilage mucous glands are also present. The stratified squamous epithelium ceases at the anterior end of the inner turbinate bone and at the inferior nasal duct.

The respiratory region possesses a simple pseudostratified, ciliated epithelium having two strata of nuclei and provided with goblet cells; the direction of the ciliate movement is toward the posterior nares. Numerous leucocytes are usually found in the epithelium and in the underlying mucosa. Branched alveolar glands, having mucous and serous alveoli, are here present. Within the mucosa are highly developed vascular plexuses, more especially of a venous character. The accessory cavities are likewise lined by ciliated epithelium, the ciliate movement being directed externally.

The olfactory region is principally confined to the superior turbinate bone and to the nasal septum lying opposite, although in the immediate vicinity of the olfactory region a few small islands of the same epithelial type are found, either entirely isolated or connected with the principal region by narrow bridges. In a fresh condition the olfactory region may be differentiated from the surrounding tissue by its color, which is distinctly yellow in man. Its pigment is contained within the sustentacular cells described on the next page.

The epithelium of the olfactory region is of the columnar pseudostratified type, with several strata of nuclei, and consequently closely simulates a stratified columnar epithelium. Here we distinguish olfactory cells and sustentacular cells.

The olfactory cells occupy a peculiar position among the cells. of special sense in that they represent true ganglion cells (von Lenhossék). Within the epithelial layer they appear as spindleshaped cells, with a spheric nucleus provided with a large nucleolus lying in the thickest portion of each cell. The nuclei of the different cells lie at varying levels in the middle stratum of the epithelial

layer. Toward the nasal cavity, the cells terminate in blunt cones, upon each of which are several stiff hairs, the olfactory hairs. The basilar ends form true centripetal nerve-processes, neuraxes, which end in the peculiar telodendria constituting the glomeruli of the olfactory bulb. (See p. 379.)

The nuclei of the sustentacular cells are more oval and are situated at nearly the same level. Toward the surface, each cell is provided with a narrow cuticular zone, while toward the basement membrane, it terminates in two or more pedicles. Between the basilar ends of these cells we find a layer of elements the broad nucleated bodies of which rest on the basement membrane, while their upper extremities terminate in short superficial processes.

The mucosa contains a large number of leucocytes as well as numerous branched alveolar glands, the so-called glands of BowIn man these are albuminous (serous) glands, and their cells sometimes contain pigment.

Jacobson's organ contains no typical olfactory cells in the human

being.

The capillaries spread out immediately beneath the basement membrane of the epithelium. In the submucous connective tissue, we find a relatively well developed vascular plexus, rich in venous vessels; this plexus is especially marked at the posterior portion of the inferior turbinate bone, forming here a tissue which resembles erectile tissue.

A dense network of lymphatics ramifies throughout the mucous membrane, carrying the lymph to the pharynx and palate. These lymph-vessels may be injected through the subarachnoid space (Key and Retzius).

The nerves (trigeminal) are widely distributed in the epithelium, ramifying through both the respiratory and olfactory regions. After repeated divisions these nerves lose their medullary sheaths, and end in telodendria which are usually provided with terminal nodules, although some are found which end in mere filaments.

TECHNIC.

337. The nasal mucous membrane is fixed in situ with osmic acid or one of its mixtures, after which small pieces are removed. It should be mentioned that the nonmedullated fibers of the olfactory nerve assume a brownish color under this treatment, while the fibers of Remak do not (Ranvier, 89).

338. In order to isolate the epithelial elements, pieces of the mucous membrane are treated with the 3 alcohol of Ranvier. But since the prolongations of the olfactory cells (neuraxes) shrivel and curl in this fluid, Ranvier recommends that, after the epithelial cells have been macerated in alcohol for one or two hours, they be treated with 1% osmic acid for a quarter of an hour. If shreds be now placed in water and teased, the cells, together with their prolongations, may be isolated without the curling of the latter.