312 ROBERT J. TERRY 



sure, just caudad, can be differentiated by its more advanced 

 state of development. At the anterior pole, cartilage formation 

 is found in connection with the suprafacial commissure. Where 

 this bar joins the cochlear capsule two regions of the capsule, 

 distinguished by their different states of development, can be 

 seen in the sections. One region, that next to the epithelial coch- 

 lear duct is composed of mesenchyma which passes peripherally 

 into precartilage. The other is a circumscribed area superim- 

 posed upon the part just mentioned. Its form is somewhat 

 circular in sagittal sections; it is composed of young cartilage. 

 This area occupies the most cephalic part of the cochlear cap- 

 sule. It can be followed medially through sections 198-192 (H. 

 E. C. ser. 492) of the anterior portion of the pars cochlearis as a 

 more or less distinct tract; further on it becomes completely fused 

 with the deeper stratum of the wall of the cavum cochleae. In 

 sections 191-186 the anterior pole of the cochlear capsule appears 

 as a simple curved plate of young cartilage. In section 185 this 

 is joined with the alicochlear commissure. The relations of the 

 cochlear capsule to the latter and to the suprafacial commissure 

 will be understood by reference to figure 8. • When traced in the 

 lateral direction, the curved plate in question goes over into the 

 suprafacial commissure, with which it conforms in the degree 

 of cartilaginous differentiation, outward size and shape. A sec- 

 ond connection between the anterior pole of the cochlear capsule 

 and basal cartilage is presented at this stage by the cartilaginous 

 basicochlear commissure, or synchondrosis, which forms the pos- 

 terior boundary of the carotid foramen. The parietal plate is 

 partly separated from the canalicular division by the foramen 

 jugulare spurium. It is continuous through young cartilage or 

 precartilage with the occipital arch and pars canalicularis posteri- 

 orly and with the commissura orbito-parietalis anteriorly. The 

 tectum posterius is represented by a short process of the lamina 

 parietalis. 



Cartilage is found in the otic capsules of a cat embryo of 15 

 mm. (fig. 7) about the walls of the semicircular ducts and the 

 vesibule, as indicated by the deep blue stain in van Wijhe prepa- 

 rations; the cochlear capsule is unstained. The basivestibular 



