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 
canals 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 
Fic. 112. Section oF THE CocHLEA OF THE CALF. X 10.—(From 
Ellenberger, after Kolliker.) 
a, Modiolus; c, scala tympani; v, scala vestibuli; Jm, 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 
