530 THE SOLIDS. 



some quantity, except where the nerves passing to it con- 

 fine it in close contact with the osseous wall. Its vestibular 

 portion consists of two sacs, viz. a principal one of trans- 

 versely oval figure and compressed laterally, called the utri- 

 culus, or common sinus, occupying the upper and back part 

 of the cavity, in contact with the fovea semi-elliptica, and 

 beneath this a smaller and more globular one, the sacculus, 

 lying in the fovea hemispherica, near the orifice of the ves- 

 tibular scala of the cochlea, and probably communicating 

 with the utriculus. 



" The membranous semicircular canals have the same names, 

 shape, and arrangement as the osseous canals which enclose 

 them, but are only a third of the diameter of the latter. As 

 the osseous canals open into the vestibule, so the membranous 

 ones open at both ends into the utriculus, there being, 

 however, a constricted neck between this sac and the ampul- 

 lated extremity of each canal. The auditory nerve sends 

 branches to the utriculus, to the sacculus, and to the am- 

 pulla of each membranous canal. These nerves enter the 

 vestibule by the minute apertures before described, and tie 

 down, as it were, both the utriculus and sacculus to the 

 osseous wall at those points, the membrane being much 

 thicker and more rigid at those parts. The branches to the 

 ampulla of the superior vertical and the horizontal semi- 

 circular canals enter the vestibule with the utricular nerve, 

 and then cross to their destinations, while that to the am- 

 pulla of the posterior vertical canal traverses the posterior 

 wall of the cavity and opens directly into the ampulla. 



" The wall of the membranous labyrinth is translucent, 

 flexible, and tough. When withdrawn from its bed and ex- 

 amined, it appears to present three coats, an outer, middle, 

 and internal. The outer is loose, easily detached, somewhat 

 flocculent, and contains more or less colouring matter disposed 

 in irregular cells exactly resembling those figured at page 22., 

 from the outer surface of the choroid coat of the eye. We 

 have not found a true epithelium on this surface. The 

 middle is the proper coat, and seems more allied to cartilage 

 than any other tissue ; its limits are well marked, it is trans- 



