DEVELOPMENT OF THE SKULL OF EMYS 743 



Of especial interest in connection with the extracolumella is 

 the processus interhyaUs described by Bender ('11) in Testudo 

 and the present writer (Kunkel '12) in Emys, extending from the 

 post ero- ventral corner medially and ventrally. From the apex 

 of the processus interhyalis a strand of dense connective tissue 

 extends ventro-medially towards the lateral aspect of the pars 

 retroarticularis of Meckel's cartilage as Fuchs ('07) has described. 

 This process, in earlier stages, is distinct from the extracolu- 

 mella as the interhyale. 



The origin of the columella auris from two separate centers is 

 also clearly shown in an embryo of 7 mm. carapace length. As I 

 have shown in an earlier paper (Kunkel '12) in this embryo the 

 insertion piece, corresponding to the extracolumella, isdistinot 

 from the stalk, which, together with the foot plate, represents the 

 stapes (col., fig. 21). Noack's conclusion ('07) that the columella 

 of chelonians is a derivative of the capsular wall is not confirmed 

 by my observations. In one of my earher stages (carapace length, 

 5.2 mm.) the blastema of the columella is distinctly in the pre- 

 chondrial stage while that of the capsule has not proceeded so 

 far. In this embryo the stapes extends medially as far as the 

 lateral wall of the otic sac and is represented by a mass of pre- 

 chondrium far in advance in development of any in its immediate 

 neighborhood. 



The relation of the nervus faciahs to the columella, I find is 

 essentially as Noack has described. The ramus hyomandibularis 

 extends caudally in a straight line from the gangUon geniculi, 

 dorsal to the stem of the columella, to the muscles which it in- 

 nervates. Ahnost immediately behind the columella it gives off 

 laterally the chorda tjaiipani which passes first in a lateral direc- 

 tion as far as the quadratum and then curves forward, crossing 

 the columella on its dorsal side, and then turns ventrally in front 

 of the Eustachian tube eventually to reach the mandible. 



Meckel's cartilage is of strong form, tapering regularly from the 

 condyle anteriorly. In cross section in front of the condyle it 

 is elliptical with the long axis of the ellipse oblique from dorso- 

 lateral to ventro-medial. At the condyle the rami of the mandi- 

 ble are flattened considerably as if by pressure from above so 



