226 ELEMENTS OF MAMMALIAN ANATOMY. 



A lymphoid fluid, the perilymph, floats the delicate mem- 

 branous internal ear within its bony cavity, while within 

 the membrane is a similar fluid, the endolymph. The vesti- 

 bule is a small sac adjacent to the tympanum, and may be 

 seen by looking through the fenestra ovalis. From the 

 dorso-caudal aspect of the vestibule, arch three semicircular 

 cunals at nearly right angles to one another. The external 

 semicircular canal is in a horizontal plane and surrounds a 

 small fossa almost caudad of the fenestra ovalis. The 

 superior semicircular canal lies in a transverse plane caudad 



FIG. 112. SECTION OF THE COCHLEA OF THE CALF. X 10. (From 

 Ellenberger, after Kolliker.} 



a, Modiolus ; c, scala tympani ; v, scala vestibuli ; Im, lamina spiralis ; pt, 

 portion of the petrous bone ; r, scala media, or ductus cochlearis. 



to the preceding. The posterior semicircular canal lies in a 

 vertical longitudinal plane, immediately laterad from the 

 jugular foramen. 



The cochlea is a coiled canal lying within the coiled 

 cavity, the bony cochlea, extending craniad from the vesti- 

 bule. If both chambers of the auditory bulla are removed 

 and a bristle thrust into the fenestra rotundum (Fig. 17), 

 it will enter the basal whorl of the bony cochlea. A line 

 drawn from the lateral margin of the foramen ovale to the 



