362 



F. H. EDGEWORTH 



It is not yet chondrified and not continuous with the trabecula 

 or parachordal. In an 11 mm. embryo the primordium has 

 separated into Quadrate and Meckel's cartilage, which are 

 chondrified. The Quadrate is continuous with the junction of 

 the trabecula and parachordal by a cartilaginous basal process, 

 and also has ascending and otic processes which are continuous 



Text-figs. 31, 32. 



Embryo 13 mm., transverse sections ; Text-fig. 32 is 42 /n behind 

 Text-fig. 31. 



ard. card, v:^ Vl'3' 

 Rhyonumd. yii 



Lot. dorsad aorta 



Ceratohycd, 



with the trabecular wall and otic capsule. The upper ends of 

 these processes are not chondrified until the 13 mm. stage. 

 I have not seen any pterygoid process of the Quadrate in any 

 one of several embryos of 11 and 12 mm. in length. The 

 structures are depicted in Text-figs. 33 and 34 from a 13-5 mm. 

 embryo. The observations thus confirm those of Sewertzoff. 

 In a 13 mm. embryo (Text-figs. 31, 32) the Ceratohyal passes 

 upwards and backwards in the hyoid segment. From the top 

 of the Ceratohyal a curved tract of cells, the Epihyal, passes 



