754 B. W. KUNKEL 



culare, an ossification of the proximal end of Meckel's cartilage, 

 is not apparent in an Eniys embryo having a carapace length of 

 11 mm. 



The den tale (d.) has the form of a long, slender plate exhibiting 

 in general a concave medial and convex lateral sm-face. It is 

 provided with flattened flanges extending both laterally and 

 medially from the dorsal margin. It Ues lateral to Meckel's 

 cartilage for almost the entire distance from the anterior, distal 

 end to the fovea articularis, overlapping with its posterior end 

 the anterior end of the supra-angulare so that the latter is inter- 

 posed between the dentale and Meckel's cartilage. 



By reason of the medial projection of the dorsal margin of 

 the dentale, this bone comes to arch in dorsally the sulcus pri- 

 mordialis which acconmiodates Meckel's cartilage. Beneath the 

 lateral flange of the dentale extends the portio alveolaris inferior 

 of the ramus mandibularis n. trigemini which gains access to this 

 groove (sulcus alveolaris inferior) from the sulcus primordialis 

 through the foramen canahs alveolaris inferioris. This foramen 

 is situated near the posterior end of the dentale immediately 

 ventral to the thickened dorsal margin. In older embryos the 

 sulcus alveolaris inferior becomes converted into the closed 

 canalis alveolaris inferior by the fiu-ther rolling over of the lateral 

 margin of the dorsal flange. 



The supra-angulare (sa.) is a small elongate plate of bone which 

 lies along the lateral aspect of Meckel's cartilage in its proximal 

 portion. It exhibits a slender posterior projection which lies 

 along the lateral side of the fovea articularis. The anterior third 

 of the supra-angulare at this stage is overlapped laterally by the 

 posterior end of the dentale. The ramus recurrens cutaneus 

 mandibulae from the mandibular branch of the trigeminus 

 passes obliquely backward along the dorsal margin of the supra- 

 angulare and somewhat medial to it. 



The angulare (a.) is a long slender plate of bone lying on the 

 ventral side of the posterior end of Meckel's cartilage in the 

 region of the supra-angulare. It forms, accordingly, the floor of 

 the sulcus primordiahs in its posterior part. It is much shorter 

 than the supra-angulare and extends neither as far anteriorly 



