THE INTERNAL EAR. 483 



macula utriculi the epithelium of the utriculus is high columnar in 

 type ; in the remaining portion it consists of a single layer of low 

 columnar cells, with a distinct basement membrane ; the epithelium 

 of the macula itself is also high, and is composed of two kinds of 

 elements of sustentacular elements and of the so-called auditory 

 hair-cells. The sustentacular cells are tall epithelial cells resting 

 on the basement membrane by means of their single or cleft basal 

 plates. Each possesses an oval nucleus lying at or beneath the 

 center of the cell. The hair-cells are peculiar cylindric elements 

 with somewhat thickened and rounded bases. One end extends to 

 the surface of the epithelium, while the other, which contains the 

 nucleus, extends only to the center of the epithelial layer. The free 

 end is provided with a cuticular zone supporting a number of 

 long, stiff hairs, which often coalesce to form single threads. On 

 the surface of the epithelium, which must be regarded as a 

 neuro-epithelium, are crystals of calcium carbonate, known as oto- 

 liths, each of which incloses a minute central vacuole (Schwalbe). 

 The otoliths are inclosed in a homogeneous substance, the otolithic 

 membrane, which coagulates in a network of filaments when sub- 

 jected to the action of fixing agents. 



The nerve-fibers going to the macula penetrate the wall, and, 

 under the epithelium, undergo dichotomous division, and, after fur- 

 ther division, form, in the region of the basilar ends of the auditory 

 cells, a plexus consisting of fine ramifications, and embracing the 

 lower ends of the auditory cells. A few fibers extend still further 

 upward, where their telodendria enter into intimate relations with 

 the acoustic cells (v. Lenhossek, 94, i). 



The structure of the sacculus is in every respect like that of the 

 utriculus, and a further description of it is therefore unnecessary. 



2. THE SEMICIRCULAR CANALS. 



The membranous semicircular canals are attached at their con- 

 vex surfaces to the periosteum of the bony canals, which they only 

 partly fill, the remaining cavity being occupied by an eccentrically 

 situated perilymphatic space traversed by connective-tissue trabeculae. 

 The walls of the perilymphatic spaces of the semicircular canals, 

 like those surrounding the utriculus and the sacculus, are lined by 

 endothelium, which covers, on the one hand, the periosteal surface 

 of the bony semicircular canals, and, on the other hand, the outer 

 wall of the membranous canals, together with the connective-tissue 

 trabeculae. The connective-tissue walls of the membranous canals 

 are structurally similar to those of the utriculus and sacculus. 

 Hensen compares their structure to that of the substantia propria 

 of the cornea. In the adult, the inner layer of the wall of the 

 canals supports here and there papillary elevations, which, however, 



