

Nerve fibers passing out 

 Ganglion Spiral between the two layers of 

 le ; fibers the lamina spiralis ossea 



PERIPHERAL TERMINATIONS OF NERVES OF GENERAL SENSATIONS 1059 



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 cen- 

 tralis, and the nerves bend outward to 

 pass between the lamellae 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 Corti's 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). 



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 mem- 

 brane. 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. 



Fia. 933. Part of the cochlear division of the acoustic 

 nerve, highly, magnified. (Henle.) 



PERIPHERAL TERMINATIONS OF NERVES OF GENERAL SENSATIONS. 



The peripheral terminations of the nerves associated with general sensations, i. e., the mus- 

 cular 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 papillae 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 fibrillae. Finally, the 

 axis-cylinder breaks up into its constituent fibrillae 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 pig's snout, where the fibrillse 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 fibrillse 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. 



