396 



THE BABBIT. 



The body of the vestibule is partially divided by a constric- 

 tion into a larger division, the utriculus, with which the semi- 

 circular canals are connected ; and a smaller division, the sac- 

 culus, which opens through a narrow neck, the canalis reunions, 

 into the cochlear canal, EL. This latter is a tube of fairly 



ER 



EP 



EC 



AC 



FIG. 159. A transverse section across the head of a Babbit Embryo of the 

 fifteenth day, passing through the medulla oblongata, the ears, and the 

 pharynx. The plane of section of the left side of the figure is slightly 

 anterior to that of the right side, x 16. 



AC, carotid artery, giving off a small branch which runs through the arch of the 

 stapes. CH, notochord. EB, tympanic membrane. EC, cartilaginous auditory 

 capsule. ED, common stem of the two vertical semicircular canals. EH, external or 

 horizontal semicircular canal. EL, cochlear canal. EO, external auditory meatus. 

 EP, posterior vertical semicircular canal. EB., recessus vestibuli. ES, Eustaehian 

 passage. EX, external ear. MA, malleus. SA, stapes. TP, pharynx. VF, fourth 

 ventricle. VJ, jugular vein. VII, facial or seventh cranial nerve. 



uniform diameter, curved as shown in the figure, and with its 

 wall markedly thicker along the inner than the outer side of 

 the curve. A cartilaginous periotic capsule, EC, is present, sur- 

 rounding the ear, but at some little distance from it ; the re- 

 cessus vestibuli alone projecting beyond the capsule. 



