178 



GENERAL STRUCTURE OF EAR. [BOOK in. 



bone of a somewhat dense character, and thus furnishes a bony 

 shell or envelope enclosing and to a large extent following the 

 contour of the complicated membranous sac. Between the outer 



- n.aud 



-s.e. 



chl 



FIG. 162. DIAGRAM TO ILLUSTRATE THE GENERAL STRUCTURE OF THE EAR. 

 (After Schwalbe.) 



The figure is purely diagrammatic, intended only to shew in one view all the 

 several important parts in relation to each other ; such a view is in the actual 

 ear impossible. 



e. the external meatus or auditory passage, in the outer part where the walls are 

 cartilaginous, m'. e. the same in the inner part where the walls are osseous. 



T. C. the tympanic cavity, t. m. the tympanic membrane, m. malleus, i. incus, 

 st. stapes, attached to the fenestra ovalis. f. r. feuestra rotunda. E. t. 

 Eustachian tube. 



U. the utricle with the perilymph space around. One semicircular canal with 

 its ampulla is shewn, with the bony core of the hoop. $. Saccule. s. e. sacculus 

 endolymphaticus lying within the cranial cavity, and connected by the ductus 

 endolymphaticus with both saccule and utricle, chl. the canalis cochlearis, con- 

 nected with the saccule by the canalis reunions, and surrounded by its 

 perilymph space, scala vestibuli, and scala tympani, the latter ending at 

 the fenestra rotunda, the former continuous with the perilymph space of the 

 vestibule around the utricle and saccule, the cochlea is shewn diagram- 

 matically as a simple curve, the scala vestibuli and scala tympani being 

 continuous at the top. 



N aud., the auditory nerve shewing the three main divisions of the trunk 



bony envelope and the inner membranous sac is developed a large 

 irregular lymphatic space which (Fig. 162) follows to a great 

 extent the contour of the sac, but is broken up by broad adhesions 

 of the membranous sac to the periosteum lining the bony envelope 

 or by narrower bridles of connective tissue crossing the space , 

 some of these form beds for the branches of the auditory nerve 

 on their way to the auditory epithelium. The fluid in this 

 space, which is lymph and which has access to the lymphatics of 

 neighbouring parts, receives the special name of perilymph. A 

 portion of the sac, with its surrounding perilymph space and bony 

 envelope, undergoes a development differing materially from that 



