PRIMORDIAL CRANIUM OF THE CAT 377 



fissure-like opening in the root of the ala as the last vestige of the 

 original gap between the anterior and middle lateral processes of 

 the pole-plate. The middle process, the synchondrosis spheno- 

 cochlearis lateralis, is, in its caudal half, the part named by 

 Fischer in a later stage the 'trabecula alacochlearis.' Noorden- 

 bos has shown, however, that the trabecula alacochlearis geneti- 

 cally has its anterior connection, not with the ala, but with the 

 basisphenoid, and only secondarily unites with the hinder mar- 

 gin of the root of the ala temporalis. 



Let us consider now, the development of the ala temporalis in 

 the cat and compare it with that of the mole, taking as a point 

 of departure the stage of 17 mm. In the cat there arises from the 

 side of the sella turcica, a precartilaginous bar, which bends about 

 the carotid artery, its anterior limb (processus alaris) crossing 

 transversely in front of the vessel, its posterior Hmb (commissura 

 ahcochlearis) extending backward upon the side of the artery 

 and joining the cochlear capsule. Here, then, are elements 

 present in both mole and cat which are in agreement in several 

 important relations. In order further to identify this combined 

 alar process and alicochlear commissm^e of cat with the middle 

 process of mole, it should be recalled that it is derived from the 

 coiTonissural element of the earUest stage (12 m.m.) the relations 

 of which to the base of the cranium, to the cochlear capsule and 

 to the' carotid artery are equivalent to the relations of the middle 

 process of mole at its first appearance (12 to 13 mm.). Compar- 

 ing, next, the relations of the middle process of mole and the 

 precartilaginous derivative of the commissural element in cat, 

 with parts lying laterally, there is present in each case an ele- 

 ment, separate from the process under consideration, related to 

 the semilunar ganglion. In Talpa this element, derived from 

 the anterior process, grows out alongside the anterior limb of the 

 middle process, from which, however, it is at first separate. It 

 is noteworthy that the -former extends somewhat caudally as 

 well as laterally, and, in conformity therewith, the space inter- 

 vening between it and the middle process extends from behind, 

 forward and medialward. In embryos of 20 to 25 mm. these 

 two^ pieces of the ala temporalis unite, the anterior limb of the 



JOURNAi OF MORPHOLOGY, VOL. 29, NO. 2 



