DEVELOPMENT OF THE EAR. 



Fig. 107. TRANSVERSE AND SLIGHTLY OBLIQUE SECTION OF THE HEAD OF A FCETAL SHEEP. IN THE 

 REGION OF THE HIND BRAIN. (From Foster and Balfour after Boettcher. ) 



HB, inner surface of the thickened \valls of the hind brain ; EB, recess of the vestibule ; YB, 

 commencing vertical semicircular canal ; CC, canal of the cochlea ; GC, cochlear ganglion of the right 

 side ; on the left side. G', the ganglion, and N, the auditory nerve connected with the hind brain. 



Fig. 108. TRANSVERSE SECTION OF 



THE HEAD OF A FCETAL SHEEP OF 

 FOUR-FIFTHS OF AN INCH IN LENGTH. 



(From Foster and Balfour after 

 Boettcher.) 



EY, recessus vestibuli ; YB, vertical 

 semicircular canal ; CC, cochlear 

 canal ; G, cochlear ganglion ; HB, 

 horizontal canal. 



organ. This coiling, however, 

 only occurs in mammals ; in 

 birds, the cochlea is a short 

 straight blind tube. 



All these parts of the laby- 

 rinth are, when first formed, 

 simple epithelial tubes sur- 

 rounded by and imbedded in 

 embryonic connective tissue. 

 As development proceeds, and 

 the skull begins to form, a 

 cartilaginous capsule becomes 

 developed around the several 

 parts of the labyrinth, and 

 this at length becomes ossified. 

 The cartilaginous capsule does 

 not closely invest the epithelial structures ; they are immediately surrounded by 

 embryonic connective tissue, which forms an internal periosteal lining to the capsule 

 and a special covering to the epithelial tube. These two connective tissue membranes 

 are everywhere separated from one another by gelatinous connective tissue, composed 



c.c 



