THE ORGANS OF THE OUTER GEEM-LAYER. 



501 



gelatinous tissue, a large spacefilled with perilymph, which is indicated 

 in the diagram, fig. 282, in black. Here and there, however, 

 •connective-tissue cords remain running from one layer of connective 

 tissue to the other, and serving as bridges for the nerves and blood- 

 vessels which are distributed to the semicircular canals. 



Finally, a last alteration takes place in the cartilaginous envelope 



Tif . 282.— SiagTammBtic representatian of the whole organ of heEuingin IIa.n, from Wiedeesheim. 



Outer ear: M^ My auricle; Mae, meatus auditorius externus; 0, its wall; Mt, membraua 

 tympani. Middle ear: Ct, Ct, cavum tympani ; 0', its wall; SAp, sound-conducting 

 apparatus, which is drawn aa a simple rod -like body in place of the auditory ossicles ; the 

 place + corresponds to the stapedial plate, which closes the fenestra ovalis ; 2*6, tuba 

 Bustachii ; T6', its opening into the pharynx; 0", its wall. Inner ear: Ihe bony labyrinth 

 (KL, KL^) for the most part cut away ; S, sacculus ; o, h, the two vertical ixjtmbra lous and 

 osseous semicircular canals; S.e, D.e, sacous and ductus eudolymphaticus, of which the 

 latter is divided at 2 into two arms ; Cp, cavum perilymphaticum ; Cr, canaljs reunions ; 

 Con, membranous cochlea, which produces at + the vestibular coecum ; Core', bony cochlea ; 

 Sv and St, scala vestibuli and scala tympani, which at * communicate with each other at the 

 cupula terminalis fjOt) ; B.p, ductus perilymphaticus, which arises from the scala tympani 

 at d and opens out at D.p^. The horizontal semicircular canal is not specially designated, 

 but is easily recognisable. 



by its becoming converted into bone-substance by endochondral 

 •ossification. Thus the membranous semicircular canals are enclosed 

 in the bony semicircular canals (fig. 282 a and h KL), which are 

 enlarged reproductions of the former. 



Corresponding changes, (fig. 282) are also accomplished in the 

 periphery of the utriculus and sacculus {S), and lead to the formation 

 of (1) a perilymphatic space {Gp), which is in communication with 



