VIEW OF THEIR ANATOMY AND DEVELOPMENT. 133 



undergo obliteration in adult Birds. I have myself frequently 

 found only a narrow tube at this point. 



Fig. 319 III. represents the type of the labyrinth in Mam- 

 mals ; here the semicircular canals and the cochlear portion 

 communicate with one another only through the intermedia- 

 tion of the aquceductus. vestibuli (R) (Bottcher, 3). See the 

 preceding chapter. The ductus cochlearis ((7) has undergone 

 extraordinary development, and forms the principal part of the 

 labyrinth ; as is already seen in Birds, it has become entirely 

 distinct from the sacculus, and is only in connection with it 

 by the narrow canalis reuniens (Cr). The canalis reunions pro- 

 ceeds from the wall of the ductus the membrana Reissneri 

 (see below) ; it opens into the cochlear passage almost at a right 

 angle, so that a small caeca! sac exists beyond its point of at- 

 tachment the vestibular caecal sac (F) (Reich ert). The other 

 end of the duct likewise terminates blindly, forming the ccecal 

 sac of the cupola (K) (Reichert). The canalis reuniens and 

 the two csecal sacs are lined by a short columnar epithelium, 

 and receive no fibres from the auditory nerve. The cochlear 

 canal, which here properly answers to its name, is wound spi- 

 rally around a bony axis, the modiolus. The number of turns 

 varies in different animals from one and a half to five. They 

 sometimes lie nearly in one plane, like the shell of the Planorbis 

 (Cetacea); sometimes, on the other hand, they may coil steeply 

 around the modiolus, as in Clausilia (Guinea-pigs) ; we may 

 thus have flat and steep coiled cochleae. 



Whilst I refer to the preceding chapter for an account of 

 the sacculus, I consider it to be advantageous in regard to 

 the somewhat complicated structure of the cochlea to precede 

 its histological description by,a short account of the bony cap- 

 sale and of the position of the ductus cochlearis, together with a 

 sketch of its development. I shall commence with the cochlea 

 of Mammals and of Man. 



A median section carried through the axis of the human 

 cochlea, as in fig. 320, exhibits a tubular canal imbedded in the 

 hard mass of the temporal bone, which, constantly becoming 

 narrower, runs spirally to the apex of an also gradually attenu- 

 ating axis, and terminates by a blind extremity in the so-called 

 cupola. This canal is traversed throughout its whole length by 



