HISTOLOGY OF THE MEMBRANOUS LABYRINTH. 87 



gelatinous tissue in such a manner that the larger branches 

 appear in sections made in the direction of the long axis of a 

 semicircular canal, whilst the secondary branches run in a 

 more or less transverse or oblique direction. Of the two larger 

 vessels (see fig. 297) which constantly run with some interval 

 between them, I regard the smaller as the artery and the larger 

 as the vein. In the formation of the cavities or lumina 

 of the tubes, the periosteum and the nucleated connective 

 tissue surrounding the vessels which traverse the cavity, may 

 be regarded as the results of the regressive metamorphosis 



Fig. 297. 



Fig. 297. Transverse section of a cartilaginous and membranous 

 semicircular canal of a foetus. 1, Cartilaginous semicircular canal ; 

 2, gelatinous tissue, which completely fills the space between the two 

 canals; 3, vein ; 4, artery ; 5, wall of the membranous semicircular 

 canal. 



of the gelatinous tissue, and as constituting the ultimate 

 products of its development. 



In the adult human subject the periosteum lining the osseous 

 labyrinth is a moderately thick layer of connective tissue inter- 

 mingled with fine elastic fibres. Both it and the vessels it 

 encloses are continuous with those of the bone, so that it is 

 difficult to detach it from the bone. The internal surface of the 

 periosteum in the semicircular canals is uneven. Rather large 

 nuclei are scattered through its substance, which become more 

 numerous, and are less regularly arranged, near the free than 



