366 ROBERT J. TERRY 



do show a certain agreement with conditions observed in the 

 lower groups. The tendency to subdivision of the vestibule 

 into anterior and posterior rooms is strongly suggestive of 

 the conformation of the cavum vestibulare in Lacerta, as de- 

 scribed by Gaupp. The contents of the anterior and posterior 

 vestibular cavities in the cat appear to be comparable with the 

 parts contained in the cavum vestibulare anterius and cavum 

 vestibulare posterius of lizard. The anterior and posterior 

 acustic foramina in lizard and cat are similarly related to the 

 vestibular cavities. Furthermore the relative positions of the 

 two spaces, one to the other, and to the otic capsule as a whole, 

 are strikingly similar in the two forms. Such a comparison must 

 accept of necessity the homology of the boundary structure be- 

 tween the vestibular cavities. In the cat this is the medial ward 

 projecting ventral part of the massa angularis, the part desig- 

 nated crista intervestibularis. In the lizard it is the septum 

 inter vestibulare. Gaupp describes the latter as a transverse 

 vertical partition between the two vestibular cavities, presenting 

 a lateral opening filled with membrane and a medial foramen for 

 the utriculus. The crista intervestibularis is hkewise transverse 

 in position, but it cannot be called a partition since it fails to 

 extend entirely across, between the anterior and posterior cavi- 

 ties. While it possesses no opening, yet, by its failure to reach 

 the medial vestibular wall, a space is left between the latter 

 and the free medial edge of the crista, by which the anterior 

 and posterior cavities are put into communication and which is 

 occupied by the utriculus. 



Lamina parietalis and tectum posterius. Decker ('83) found the 

 parietal plates in cat embryos of 5.5 to 6.1 cm. bent inward, which 

 is not the case in the younger embryos of the present study; 

 rather, the dorsal, irregular margins are turned a little laterally. 

 Decker's observation is interesting in proving that the parietal 

 plate participates in the cranial roof, to only a sUght extent, as 

 his figure shows, but, nevertheless, marking an unusual develop- 

 ment of this part of the cranial wall for mammals. The lamina 

 supracapsularis of Echidna, remarkable for its great breadth and 

 its continuity with the ear capsule, is, in its anterior part, com- 



