542 



ORGAN OF HEARING. 



the terminations of the cochlear nerve is also 

 applicable here. The filaments of the nerves 

 of the common sinus and saccule expand in a 

 fan-like manner on their walls, and having pe- 

 netrated them, are resolved into a nervous layer 

 like the retina, situated on the inner surface of 

 the walls of those cavities. This nervous layer 

 is, in the human ear, pervaded by extremely 

 minute transparent fibres. In the rabbit I have 

 distinctly seen, with a doublet magnifying 150 

 diameters, a fibrous or tubular structure similar 

 to that of the retina first discovered by Ehren- 

 berg. 



As regards the entrance of the nerves of the 

 ampullae, Steifensand* gives a similar but more 

 detailed account than Breschet. He says, the 

 nerve, after having embraced in a forked man- 

 ner about a third of the circumference of the 

 ampulla, enters the wall of it. 



Resolving itself now into infinitely fine fila- 

 ments, the nerve penetrates the septum which 

 lies quite close to the opening in the common 

 sinus, and which resembles a semi lunar emi- 

 nence projecting into the interior. It now 

 covers the surface of the septum and a circum- 

 scribed portion of the adjacent inner surface of 

 the wall of the ampulla with an extremely deli- 

 cate nervous pulp. The two ends of the semi- 

 lunar septum, gradually flattening and spread- 



Fig. 242. 



Common sinus, together with the ampullae and semi- 

 circular tubes, and the entrance of the nerves into 

 them. (From Steifensand.) 



Fig. 243. 



The ampullae of the superior and horisontal semi- 

 circular tubes, with a part of the common sinus. The 

 fan-like expansion of the nervous fibrils on the latter 

 is seen, and also the fork-like expansion of the nerves 

 on the outer surface of the ampulles. Magnified. 

 (From Steifensand.) 



* MuUer's Archiv. fur Anatomie, Physiologic, 

 und wissenschaftliche Medecin, 1835. Heft. ii. 

 s. 174 and 184. 



ing out, lose themselves in the wall of the am- 

 pulla. 



Fig. 244. Fig. 246. 



Fig. 245. 



Fig. 244, (from Steifensand.) The ampulla 

 opened in order to exhibit the septum. 



Fig. 245, (from Steifensand.) The fork-like ter- 

 mination of the nerve of the ampulla and the semilunar 

 septum, having the appearance of pure nervous sub- 

 stance. 



Fig. 246, (also from Steifensand.} The expan- 

 sion of the nervous pulp over the septum. 



Bloodvessels of the labyrinth. The prin- 

 cipal artery of the labyrinth is the arteria 

 auditiva interior. It is a branch of the basi- 

 lar. It enters the internal auditory meatus 

 along with the nerve of the seventh pair, and 

 at the bottom of it divides into two branches, 

 the cochlear and vestibular arteries, which 

 enter the labyrinth with the corresponding 

 nervous filaments. 



The cochlear artery, arteria cochlea, divides 

 into a number of branches which enter the 

 cochlea by the spiral tract of holes ; one in par- 

 ticular, arteria centralis modioli, passes through 

 the central canal of the axis as far as the apex 

 of the cochlea. 



The vessels of the walls of the cochlea are 

 more numerous in the scala vestibuli than in 

 the scala tympani. The arterial branches on 

 the spiral lamina anastomose with each other 

 at the outer margin of the osseous zone. From 

 the convexity of the anastomotic arches nume- 

 rous small arteries arise and run parallel as far 

 as the outer margin of the middle zone, where 

 they again anastomose, forming loops infinitely 

 smaller, from the convexity of which capillary 

 vessels run. These capillary vessels terminate 

 in a sinus of a venous nature, lodged in the 

 substance of the outer margin of the spiral 

 lamina. 



The vestibular artery, arteria vestibuli, sup- 

 plies the vestibule and semicircular canals to- 

 gether with their contents, the saccule, common 

 sinus, ampullae, and semicircular tubes, and 

 sends a branch along the surface of the spiral 

 lamina corresponding to the vestibular scala. 

 The stylo-mastoid artery, a branch of the poste- 

 rior auricular, sends a twig to the external 

 semicircular canal. The occipital artery also 

 frequently sends twigs to the labyrinth. 



The bloodvessels form a beautiful plexus on 

 the ampulla?, and considerable trunks run along 

 the whole length of the semicircular tubes, sup- 

 ported on their surface by a delicate cellular 

 tissue, which forms the vehicle for the passage 

 of the small lateral branches given off to the 

 walls of the tubes. 



