THE EAR. 357 



other with, that of the tympanum. This membrane consists of 

 several layers of cylindrical epithelial cells, the upper or inner 

 of which have their broad surfaces directed inward and carry 

 cilia. In the other layers the epithelia are wedge-shaped. The 

 epithelium rests upon a basement-membrane, beneath which is 

 a layer of connective tissue (Fig. 159, 5), in which lie the muci- 

 parous glands (Fig. 159, 6, 7), which are similar to those of 

 the pharynx and oesophagus, and lined with wedge-shaped 

 epithelium. These glands are absent in the safety-tube. A 

 plexus of nerves arising from the pharyngeal and tympanic 

 plexuses has been demonstrated, the final distribution of which 

 to the glands is probable. 



Before leaving the middle ear a short mention of the os 

 sicula and their mode of articulation is in place. The bones 

 are composed of an internal spongy and an external compact 

 portion. The former is very rich in blood-vessels. These 

 bones are covered in early life by the mucous membrane only, 

 but in later life there is also a thin periosteum to be seen. 

 Their articulation with each other is constructed similarly to 

 that of the larger joints; i.e., their articular ends are sur- 

 rounded by a capsule in which is a synovial fluid. The method 

 of union of the foot- plate of the stapes with the fenestra ovale 

 is a little more complicated. The bottom and edges of the plate 

 are covered with a thin film of hyaline cartilage. The edges of 

 the window are also covered with cartilage, which is united to 

 that of the plate by means of a fine network of elastic tissue. 

 The base of the plate rests upon a firm connective-tissue layer, 

 a continuation of the periosteum lining the inside of the scala 

 tympani, and called the ligamentum baseos-stapedis. 



The muscles connected with the ossicula belong to the 

 striped variety, and are connected to the bones by tendons, 

 which are covered by the mucous membrane wherever they 

 pass through the tympanum. 



The internal ear. The internal ear consists of two portions, 

 to which the auditory nerve is finally distributed, and which 

 are the essential parts concerned in the perception of sound. 

 These are the membranous labyrinth and the cochlea. 



In man and the higher vertebrates both of these parts are 

 enclosed within bony walls, a circumstance which makes their 

 histological study a matter of considerable difficulty. In fishes, 

 however, although the cochlea is represented merely by a small 



