STRUCTURE OF THE WALL OF THE LABYRINTH. 95 



semicircular canals. (1) The layer of connective tissue ; (2) the 

 hyaline tunica propria; (3) the papilliform or villus-like pro- 

 cesses, and (4) the epithelium. 



The outer fibrous layer is composed of connective tissue 

 with numerous nuclei scattered through its substance, which for 

 the most part runs circularly around the canal, and presents 

 no particular marks distinguishing it either from the above- 

 described ligaments, or from the periosteum. Where the canal is 

 in contact with the periosteum, the outer fibrous layer is very 

 thin ; but it becomes thicker where the wall is free and attains 

 its greatest development ; that is to say, at the point where the 

 ligamenta labyrinthi canaliculorum are attached. The large 

 and for the most part rounded nuclei, owing to their mode of 

 arrangement on the outer surface of the free wall of the canal, 

 quite give the appearance of an epithelial investment. The 

 nuclei, however, have a similar disposition in the ligaments of 

 the labyrinth, and on the side of the periosteum ; so that in good 

 imbibition preparations it may be clearly seen that the outer 

 surface of the membranous canals are not really invested by 

 a layer of pavement epithelium.* 



If an examination be made of the entire semicircular 

 canal which, with the periosteum and the ligaments, has 

 been withdrawn from its natural position, another fibrous 

 plexus comes into view near the vessels, of the nature of which 

 I am still doubtful. The trabeculse of this plexus are pale and 

 moderately broad, and form regularly . arranged meshes. At 

 the nodal points they become much broader, exhibit their 

 fibrous nature more distinctly, and contain large nucleated cells 

 in their substance. At first sight this plexus presents precisely 

 the aspect of nerves with intercalated ganglion cells (fig. 303). 

 Whether they really are nerves or some other kind of tissue, 

 I &m unable at present to state with certainty. It need 

 scarcely be remarked that it would prove of great interest if 

 these turned out to be the nerves of the membranous semi- 



* According to Schwalbe and F. E. Weber, the space between the 

 membranous and the osseous labyrinth filled with perilymph is a lymph 

 space, since injections into the cavity of the arachnoid penetrate into it 

 through the poms acusticus. 



