982 GENERAL STRUCTURE OF EAR. [BOOK in. 



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 cross- 

 ing the space ; some of these form beds for the branches of the 

 auditory nerve on their way to the auditory epithelium. The 



FIG. 166. 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. 



m.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. fenestra 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. 8. Saccule. s.e. saccu- 

 lus 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 reuniens, 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 diagrammatically as a simple curve, 

 the scala vestibuli and scala tympani being continuous at the top. 



N. and. the auditory nerve shewing the three main divisions of the trunk. 



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 peri- 

 lymph space and bony envelope, undergoes a development 

 differing materially from that of the rest of the sac, and is 

 known as the cochlea. The bony envelope surrounding the 

 parts of the membranous sac known as the utricle and saccule 

 does not follow closely the contour of those parts but remains 

 an undivided part called the vestibule (Fig. 167) ; the parts of 



