100 THE MEMBRANOUS LABYRINTH, BY PROF. RUDINGER. 



are really to be regarded as part of the tunica propria. The 

 line of demarcation which, in transverse sections, occurs be- 

 tween the membrane and the papillae (fig. 302) depends only 

 upon the thickness of the section. In very fine sections no 

 contour lines are perceptible between the two, even when ex- 

 amined with high powers. If we may assume that the mem- 

 branous canals secrete the endolymph, it is obvious that the 

 papillae, quite independently of other physiological functions, 

 constitute structures that effect great extension of the surface. 



In Mammals, the walls of the membranous labyrinth are 

 much thinner than in Man. The thickness of their membranous 

 semicircular canals varies only to a slight extent, and the 

 mucous membrane has no papillae. 



In Birds, the membranous labyrinth varies in thickness in 

 the utriculus, the ampullae, and to a remarkable extent in the 

 semicircular canals. Where the canals, which appear oval on 

 section, are adherent to the osseous wall, they are extremely 

 thin; but the thickness of their wall gradually increases 

 towards the unattached part of their periphery. The thinnest 

 part has a diameter of 0'020, and the thickest of O'OSO of a 

 millimeter. I cannot corroborate the statement of Hasse, that 

 the thickness of the walls varies within small limits, and that 

 no constant can be given for particular regions. According to 

 my observation, the thin portion of the wall of the canals is 

 completely limited to the surface attached to the periosteum ; 

 whilst the thick portion, which moreover presents a groove for 

 the reception of the larger vascular branches, is turned away 

 from the bone. 



The connective tissue present in the osseous canal is the only 

 representative of a fibrous layer on their external surface. 

 The thick tunica propria, which, in conjunction with the epi- 

 thelium on the basement membrane of the inner surface, forms 

 the wall, has been described in Birds, Fishes, and Reptiles, as the 

 " Labyrinth Cartilage." In the important treatises of Leydig, 

 Deiters, and Hasse, exact descriptions with illustrations will 

 be found of the histology of the wall of the canal. Elongated 

 or polygonal small stellate nuclei are distributed somewhat 

 sparingly through a structureless matrix which only presents 

 a finely granular appearance in specimens that have been pre- 



