MUCOUS MEMBRANE OF THE EUSTACHIAN TUBE. 79 



In the Horse, the wide safety tube is separated from the 

 accessory fissure by a thick process of the mucous membrane. 

 The latter opens into the air sac. This stretches throughout 

 almost the whole length of the Eustachian tube, and the air 



Fig. 293. 



Fig. 293. Mucous membrane of the accessory fissure of Man, 

 showing the- parietal folds and glands. 1, Prominent folds of the 

 mucous membrane, with an epithelium and a subjacent fibrous 

 layer, which last contains many nuclei ; 2, submucous fibrous layer ; 

 3, acinous glands ; 4, excretory ducts of the glands, lined by 

 transitional epithelium ; 5, ciliated epithelium on the lateral wall. 



sacs of the two tubes reach to the middle line in front of 

 the vertebral column, and are bounded by the base of the 

 skull and the transverse processes of the two first cervical 

 vertebrae. 



