398 SPECIAL PHYSIOLOGY. 



larger one, of an oblong form, called the common sinus or utricle, 

 placed near the openings of the semicircular canals. In the interior 

 of the semicircular canals, are three membranous semicircular canals ; 

 they are of the same form as the bony canals in which they are in- 

 closed, having their respective ampullae, and opening into the utricle 

 by five orifices. 



The walls of the membranous labyrinth, are firm and semi-trans- 

 parent : they consist of three layers ; the outer one is a loose vascular 

 structure, containing pigment cells ; the inner one consists of polygo- 

 nal epithelial cells; the intermediate layer is a thick glassy- looking 

 fibrous tunic. The saccule, utricle, and membranous canals, contain 

 a limpid, slightly albuminous fluid, called the endolymph. Within the 

 walls of the saccule and utricle, are two roundish clusters of solid 

 imperfectly crystalline particles of mixed carbonate and phosphate of 

 lime, called otoliths or otoconia, that is, ear-stones or ear-sand; the 

 otoliths are connected with the fine ends of the vestibular branch of 

 the auditory nerve, to be presently described. In the membranous 

 canals and ampullae, a few scattered particles of the same calcareous 

 mutter, are also found. The otoconia, or ear-sand, is wanting in some 

 persons. 



The interval between the inner walls of the osseous labyrinth and 

 its membranous sacs and semicircular canals, as well as the scala of 

 the cochlea, in which there are no membranous sacs or canals, is occu- 

 pied by a thin, slightly albuminous fluid, called the perilymph or liquor 

 Cotunnii; it resembles in composition, the endolymph just named, and 

 is secreted by a delicate fibro-serous membrane, which lines all the 

 inner surface of the osseous labyrinth ; it supports the sacs, the canals, 

 and the nerves distributed to these parts. 



The cochlea, moreover, presents certain peculiar microscopic struc- 

 tures, upon and within the membranous portion of its spiral partition. 

 Thus, the bony part of the lamina spiralis, presents a grooved margin, 

 the upper edge of which, viz., that corresponding with the scala vestib- 

 uli, supports a finely toothed membrane, named the zona denticulata ; 

 its lower edge being perforated for the passage of nerves, is called the 

 habenula perforata. These margins of the lamina spiralis, moreover, 

 give attachment, each to a fine layer of periosteum, the upper one of 

 which, connected with the zona denticulata, and turned towards the 

 vestibular scala, is named the membrane of Oorti ; the lower one, seen 

 in the tympanic scala, is called the basilar membrane. These two 

 membranes form the semi-transparent partition formerly known as 

 the membranous part of the lamina spiralis. Between these two lay- 

 ers is a triangular space, smaller than either of the scalge, and now 

 named the scala media (Kolliker), which is the essential auditory por- 

 tion of the cochlea, and probably contains fluid. In the scala media 

 are found two sets of minute rod-like bodies, arranged parallel with 

 each other, in a radiated position from the axis of the cochlea, named 

 the rods of Corti ; the rods of the two sets are inclined towards each 

 other above, so as to form an angle, where they appear to be connected 

 together by a fine membrane, the membrana velamentosa ; when viewed 

 from the surface of the membrane, the series of rods suggests a resem- 



