744 B. W. KUNKEL 



that each one flares out laterally to form a distinct flange. The 

 upper surface of the condylus mandibularis is saddle-shaped to 

 fit into the processus articularis of the palatoquadratuni. The 

 processus retroarticularis is very poorly developed, extending 

 only a very short distance behind the condyle as a somewhat 

 laterally compressed keel. The distal ends of the two rami of the 

 mandible are united by a strong symphysis in the form of a mod- 

 erately thin horizontal plate of triangular form which extends 

 behind the anterior ends of the rami and fills up the angle made 

 by the two. An independent 'basimandibular' element, such as 

 Parker ('80) describes in Chelone, is not present. In earher stages 

 than that modelled, the symphysis is much shorter, although sec- 

 tions in this region show the rami to be widening medially just 

 behind theii* union to fuse finally and increase the strength of 

 the symphysis. 



In the stage modelled, the proximal end of Meckel's cartilage 

 has not yet begun to ossify to form an articulare. This ossifica- 

 tion becomes evident for the first tune in an embryo having a 

 carapace length of 13.5 mm. 



In the earUest stage which I have studied (carapace length, 

 4.7 mm.) Meckel's cartilage is present as a cylindrical rod of 

 prechondrium which tapers gradually as it proceeds from its 

 articulation to its distal (anterior) end. At this stage the rami 

 do not meet in a sjaiiphysis. The processus retroarticularis is 

 relatively longer than at a later stage, possibly because the con- 

 dylus, in becoming larger, usurps a portion of the original pars 

 retroarticularis. 



HYOID AND VISCERAL ARCHES 



The developn^ent of the hyoid and visceral arches of Emys 

 has already been described by Fuchs ('10) to whose account I 

 can add from my own study of this region only a few points. 



The corpus hyale in the stage modelled is simple and of the 

 pentagonal form usual in the adult chelonians. The apex is 

 directed . anteriorly and from its lateral margins project three 

 pairs of processes. It is somewhat concave dorsally and convex 

 ventrally to form a shallow cup with a thickened rim in which the 



