Henry Gray (18251861). Anatomy of the Human Body. 1918.
the foramina in the area vestibularis inferior, and end in the macula of the saccule. The posterior branch runs through the foramen singulare at the postero-inferior part of the bottom of the meatus and divides into filaments for the supply of the ampulla of the posterior semicircular duct.
The cochlear nerve (n. cochlearis) divides into numerous filaments at the base of the modiolus; those for the basal and middle coils pass through the foramina in the tractus spiralis foraminosis, those for the apical coil through the canalis centralis, and the nerves bend outward to pass between the lamellæ of the osseous spiral lamina. Occupying the spiral canal of the modiolus is the spiral ganglion of the cochlea (ganglion of Corti) (Fig. 933), consisting of bipolar nerve cells, which constitute the cells of origin of this nerve. Reaching the outer edge of the osseous spiral lamina, the fibers of the nerve pass through the foramina in the tympanic lip; some end by arborizing around the bases of the inner hair cells, while others pass between Cortis rods and across the tunnel, to end in a similar manner in relation to the outer hair cells. The cochlear nerve gives off a vestibular branch to supply the vestibular end of the ductus cochlearis; the filaments of this branch pass through the foramina in the fossa cochlearis (page 1048).
FIG. 933 Part of the cochlear division of the acoustic nerve, highly magnified. (Henle.) (See enlarged image)
Vessels.The arteries of the labyrinth are the internal auditory, from the basilar, and the stylomastoid, from the posterior auricular. The internal auditory artery divides at the bottom of the internal acoustic meatus into two branches: cochlear and vestibular. The cochlear branch subdivides into twelve or fourteen twigs, which traverse the canals in the modiolus, and are distributed, in the form of a capillary net-work, in the lamina spiralis and basilar membrane. The vestibular branches are distributed to the utricle, saccule, and semicircular ducts.
The veins of the vestibule and semicircular canals accompany the arteries, and, receiving those of the cochlea at the base of the modiolus, unite to form the internal auditory veins which end in the posterior part of the superior petrosal sinus or in the transverse sinus.
1e. Peripheral Terminations of Nerves of General Sensations
The peripheral terminations of the nerves associated with general sensations, i. e., the muscular sense and the senses of heat, cold, pain, and pressure, are widely distributed throughout the body. These nerves may end free among the tissue elements, or in special end-organs where the terminal nerve filaments are enclosed in capsules.
Free nerve-endings occur chiefly in the epidermis and in the epithelium covering certain mucous membranes; they are well seen also in the stratified squamous epithelium of the cornea, and are also found in the root-sheaths and papillæ of the hairs, and around the bodies of the sudoriferous glands. When the nerve fiber approaches its termination, the medullary sheath suddenly disappears, leaving only the axis-cylinder surrounded by the neurolemma. After a time the fiber loses its neurolemma, and consists only of an axis-cylinder, which can be seen, in preparations stained with chloride of gold, to be made up of fine varicose fibrillæ. Finally, the axis-cylinder breaks up into its constituent fibrillæ which often present regular varicosities and anastomose with one another, and end in small knobs or disks between the epithelial cells.
Under this heading may be classed the tactile disks described by Merkel as occurring in the epidermis of the pigs snout, where the fibrillæ of the axis-cylinder end in cup-shaped disks in apposition with large epithelial cells.
The special end-organs exhibit great variety in size and shape, but have one feature in common, viz., the terminal nerve fibrillæ are enveloped by a capsule. Included in this group are the end-bulbs of Krause, the corpuscles of Grandry, of Pacini, of Golgi and Mazzoni, of Wagner and Meissner, and the neurotendinous and neuromuscular spindles.