.204 DEVELOPMENT OF THE MAHSUPIAL SKULL, 



marked. Meckel's cartilage is of large size, and has the dentary 

 lying on its outer side. 



Section G(fig.l9) shows the relation of parts at the posterior 

 end of the alisphenoid. The basal cartilage is perforated by the 

 carotid artery, and the alisphenoid lies partly below the outer 

 portion. The Gasserian ganglion is here of large size, and fills in 

 the whole space between tlie basal cartilage, the alisphenoid, and 

 the orbitosphenoid. 



Section H{fig.20) is through the anterior part of the auditory 

 capsule. The basal cartilage is a broad, fairly thick, flat plate. 

 To its outer side is attached the auditory capsule, which here 

 contains the cochlea. The anterior end of the cochlea is curved 

 outwards, and the section is across the curved portion. There is 

 no coiling as yet, the curve forming less than a semicircle, 

 nesting on the outer side of the auditory capsule is the geniculate 

 ganglion of nerve vii. A little outside of the ganglion is the 

 malleus cut in section. Below the malleus and the auditory 

 capsule is seen the Eustachian canal and tympanic cavity, and a 

 little external to this is the external auditory meatus tilled with 

 •epithelium. The orbitosphenoid is much smaller than in the 

 anterior sections. Inferiorly both the hyoid and the thyrohyal 

 cartilages are seen in section. 



Section T(Pl.xv., fig.21) is through the middle of the auditory 

 capsule. The section does not differ very greatly from the preceding 

 The upper part of the capsule is now seen united with the posterior 

 part of the orbitosphenoid bar. The utricle, saccule, and posterior 

 end of the cochlea are seen in section. Portions of the incus and 

 stapes are shown, and internally much of nerve viii., is seen. 



Section J(fig.22) is considerably further back than Section I. 

 The utricle and the ductus endolymphaticus are seen lying side 

 by side inside the upper part of the cartilaginous auditory capsule. 

 Two semicircular canals are seen in section. The lower part of 

 the auditory capsule has almost disappeared. The basal cartilage 

 is now much broader; and, in the space between it and the 

 %auditory capsule, is seen the ganglion of nerve x. On the outside 

 ■of the capsule is seen the tegmen tympani, which, in this section, 



