358 ROBERT J. TERRY 



brane bones several have still to make their appearance and 

 none of the purely endochondral ossifications is present. Talpa 

 of 27.3 mm., Semnopithecus of 53 mm., Homo of 8 cm,, in which 

 the obhquity of the principal otic axis has been recorded, are 

 all at stages of development in which bone formation is well 

 established and therefore can hardly be compared with cat 

 embryos in the stages under consideration. On the other 

 hand, obliquity of the otic axis is present in the mole of much 

 younger stages, if one can judge by the photographs of Noorden- 

 bos, and the same is true for the Sus cranium described by Mead, 

 which is at approximately the same stage as the Felis cranium 

 modeled. Again, Voit states that in Lepus the two canalicular 

 parts stand parallel, and only a shght convergence of the coch- 

 lear parts is present; the stage is one in which osseous develop- 

 ment is advanced (45 mm. gr. L.). Therefore, it appears that 

 the definitive oblique direction of the long axis of the auditory 

 capsule, typical of mammals, is attained at different periods in 

 the species considered, the tendency being toward its early 

 establishment. As in the case of the occipital region, so also 

 with the otic capsule, the position changes with the development 

 of the bony cranium. The shifting of the otic axis from a posi- 

 tion at right angles to the cranial base in the chondral stage 

 to one of marked obliquity (cephalo-ventro-mesad) in the 

 osseous stage, can hardly be a result of the straightening of the 

 cranial axis. The factors involved in influencing the change 

 must remain for future inquiry. 



Another characteristic of the position of the mammahan otic 

 capsule is its location in the base of the skull rather than i i the 

 lateral wall as is the case in increasing degree from this class 

 back to lower vertebrates. In mammals, not only does the coch- 

 lear capsule hold a basal position, but the phylogenetically 

 older canalicular part is rotated ventralward as well as caudal- 

 ward. Toward the attainment of this mammalian peculiarity 

 the cat cranium, in the stages under discussion, presents what 

 seems to be the initial steps. Though the cochlea, a phylo- 

 genetically later acquisition to the ear, asserts itself early in 

 claims for space, the relations established in the chondocranium 



