PRIMORDIAL CRANIUM OF THE CAT 305 



of the semilunar ganglion and the roots of the fifth nerve. As 

 shown by the sections, these structures are embedded in mesen- 

 chyma which extends laterally to Meckel's cartilage and medially 

 as far as the plane of the chondrocranial wall; here, in the form 

 of a membrane, it becomes fixed to the margins of the fenestra 

 sphenoparietalis. For this region the name cavum supra- 

 cochleare has been proposed by Voit. The cavum supracoch- 

 leare and the several structures therein are excluded from the 

 cavity of the chondrocranium by the membrane of the spheno- 

 parietal window. 



Cavities of the otic capsule 



A frontal section through the vestibular region shows a large 

 irregular space containing parts of the membranous labyrinth 

 (fig. 10). This space extends anteriorly into the pars cochlearis 

 as the ca\'nm cochleae, lodging the cochlear duct; posteriorly 

 into the pars canalicularis in the form of the canales semi- 

 circulares. The main room opened by the section, vestibulum, 

 contains the utricle and saccule. 



Cavum cochleae (figs. 19, 20, 21, 22). The great oval cavity 

 of the pars cochlearis, traversed by a low septum spirale, has 

 already begun to asssume the form of a winding canal. This 

 may be followed from the vestibule, wdth which it is in wide 

 communication, ventrally, then in a spiral course into the ante- 

 rior part of the cochlear capsule. At its commencement the 

 canal is quite wide, and its limiting cartilaginous walls incom- 

 plete through the presence of large openings; caudally, the 

 periljaiiphatic foramen; laterally, the fenestra vestibuU; dorsally, 

 the inferior acustic foramen. The cochlear duct makes a little 

 more than one complete turn and occupies but a small part of 

 the cavity which is elsew^here filled by young connective tissue 

 (fig. 9). This tissue extends into the perilymphatic foramen and 

 to the edge of the spiral septum where, by condensation of its 

 elements, it presents the form of a spiral membrane (fig. 22). 

 No indication of cartilage formation was observed in this mem- 

 brane in the present or in a later stage. The cartilaginous sep- 

 tum spirale takes origin in the primary floor of, the internal 



