THE MEMBRANOUS LABYRINTH. 685 



and e) over an intervening triangular space ; they slant towards each other 

 above, and are separated below like the rafters in a roof. The inner row, 

 the more numerous, are in contact with each other on the sides, and the 

 outer set touch only by the upper end. Where they touch above they are 

 flattened and directed out, the inner (d) overlapping the outer (e) ; and 

 where they rest on the membrana basilaris each is provided with a nucleus- 

 like body. 



The cells, somewhat like columnar epithelium (fig. 247), are nucleated, 

 and are arranged vertically on the sides of the rods : the lower end is fur- 

 nished with a process which directed to the membrana basilaria, and the 

 other placed upwards, is provided with stiff filaments or hairs. 



The inner set (i) stand in a single line between the sulcus spiralis and 

 the inner row of rods. The other set (j) four deep, are flattened and 

 riband-like, and bulged below, and are placed outside the external row 

 of rods ; the filaments at the upper end project through apertures in the 

 layer (f) above them. 



Lamina reticularis (/) (Kolliker). A very thin layer of flattened par- 

 ticles (phalanges) is continued over the outer half of the organ of Corti ; 

 in it are apertures, through which pass the filaments at the end of the 

 cells. And around the upper ends of the inner cells is a similar uniting 

 material. It is supposed to fix and keep in place the cells. 



An epithelial layer, consisting of cubical cells, covers the floor of the 

 space outside and inside the organ of Corti. 



The MEMBRANOUS LABYRINTH (fig. 248) is constituted of sacs, contain- 

 ing fluid, in which the auditory nerve is expanded. The sacs are two in 

 number, viz., utricle and saccule, and have the general shape of the sur- 

 roundiug bony parts ; they are confined to the vestibule and the semicir- 

 cular canals. Surrounding them is the perilymphic fluid. 



Dissection. The delicate internal sacs of the ear, with their nerves, 

 cannot be dissected except on a temporal bone which has been softened in 

 acid, and afterwards put in spirit. The previous instructions for the dis- 

 section of the osseous labyrinth will guide the student to the situation of 

 the membranous structures within it, but the surrounding softened mate- 

 rial must be removed with great care. 



A microscope will be needed for the complete examination of the sacs. 

 For the display of the bloodvessels a minute injection will be required. 



The utricle (fig. 248, c?), or the common sinus, is the larger of the two 

 sacs, and is situate at the posterior and upper part of the vestibule, oppo- 

 site the fovea semi-elliptica in the roof. It is transversely oval in form, 

 and connected with it posteriorly are three looped tubes, which are pro- 

 longed into the semicircular canals. 



These prolongations (</) are smaller than the osseous tubes, being only 

 one third of their diameter ; and the interval between the bone and the 

 membrane is filled by fluid the perilymph. In form they resemble the 

 bony cases, for they are marked at one end by a dilatation (/) corre- 

 sponding with the ampulla of the osseous tube ; and further, two are 

 blended at one end, like the canals they occupy : they communicate with 

 the utricle by five openings, and are filled with the fluid of that sac. At 

 each ampullary enlargement there is a transverse projection into the inte- 

 rior of the cavity, and at that spot a branch of the auditory nerve enters 

 the wall. 



The utricle and its offsets are filled with a clear fluid, like water, which 



