THE ORGANS OF SENSE. 24 1 



Let us fiist make a cursory sketch of the unessential acces- 

 sory parts. 



The external ear presents the auricle and the external au- 

 ditory canal. The former consists of elastic cartilage covered 

 with rarefied corium. Its muscles are transversely striated. 



The ceruminous glands of the external auditory canal have 

 been previously mentioned (p. 137). 



The drum membrane, or membrana tympani, a fibrous 

 diaphragm, is clothed externally by a rarefied cuticular cover- 

 ing, internally by the delicate mucous membrane of the tym- 

 panic cavity with simple pavement epithelium. The vascular 

 net-work of this membrane is complicated (Gerlach). Lym- 

 phatics and nerves are likewise abundant. The termination 

 of the latter is for the most part unknown. 



The entire "middle ear" is lined with a thin, vascular mu- 

 cous membrane. The vascular net-work shows a considera- 

 ble development of the venous portion. The nervus tym- 

 panicus presents ganglia. The auditory ossicles consist of 

 true compact bone substance ; their muscles are transversely 

 striated. The Eustachian tubes have stratified ciliated epithe- 

 lium and true mucous glandules. Their nerves show small 

 ganglia. 



The internal ear, as is known, consists of the vestibule, 

 the semi-circular canals and the cochlea. Vesicles filled with 

 watery lymphatic fluid occupy the cavities. The auditory 

 nerve terminates in the ampulla and in the saccules of the 

 vestibule, and then on the spiral plate of the cochlea (ramus 

 vestibuli and ramus cochleae). 



The vestibule and the inner surfaces of the semicircular 

 canals are lined with periosteum. The fluid contained in 

 their interior is called the perilymph. The periosteum and 

 the tissue of the mucous membrane of the tympanic cavity 

 combined, form the so-called membrana tympani secundaria. 

 The parietes of the saccules of the vestibule (sacculus hemi- 

 ellipticus and rotundus) and the membranous semicircular 

 canals, together with their ampullae, present externally unde- 

 veloped connective tissue, internally a hyaline nucleated layer 

 11 



