VESSELS OF THE MEMBRANOUS LABYRINTH. 107 



and moderate thickness. Their thickness amounts upon the 

 average to (H)40 of a millimeter. A few oval connective-tissue 

 corpuscles are distributed through the whitish hyaline matrix. 

 On the outer surface there are pale fibres which run through 

 about one half of the thickness of the wall, and as this stria- 

 tion occurs equally in all sections, I cannot regard it as due to 

 the accidental formation of folds. The interior is lined by a 

 large-celled pavement epithelium. 



3. THE VESSELS OF THE MEMBRANOUS LABYRINTH. 



The vessels distributed to the sacculi, the membranous semi- 

 circular canals, and the periosteum of the labyrinth, differ in 

 their arrangement in these several regions; for whilst at the 

 point of entrance of the nerves into the sacculi and ampullae 

 there is a very rich and close vascular plexus, the membranous 

 canals are surrounded by a coarse plexus with wide loops. 



The larger arteries pass to the walls of the utriculus and 

 sacculus rotundus in company with the branches of the vesti- 

 bular nerves, and form strong coarse plexuses opposite to the 

 macula and crista acustica in the loose connective tissue 

 between the bones and that part of the wall of the sacculus 

 which bears the macula acustica. On the wall of the sacculus 

 itself the capillaries become finer, and, towards the periphery of 

 the macula, form numerous loops, without however penetrating 

 the substance of the tunica propria. In Birds and Fishes, large 

 capillary loops traverse the tunica propria, and extend to the 

 basement membrane. In Man, fine capillaries reach beyond the 

 limits of the maculae acusticse and are distributed in the ex- 

 ternal fibrous layer of the wall of the sacculus, which is destitute 

 of nerves. 



Proceeding from the vestibule, large arterial branches run 

 into the osseous semicircular canals, and pursue an arched course 

 corresponding to the axis of their curvature. The vessels are 

 collectively surrounded and fixed in their position by a rela- 

 tively thick and nucleated investment, which is a residue of 

 the foetal gelatinous tissue destined for the attachment of the 

 vessels. From the larger vessels running in the centre of the 

 osseous canals finer but still tolerably thick- walled branches are 



