DEVELOPMENT OF THE SKULL OF EMYS 745 



larynx rests. The anterior apex of the corpus is produced ante- 

 riorly to form a conical processus lingualis which exhibits on its 

 dorsal surface at its proximal end a shallow longitudinal groove 

 representing the original space between the pair of processes 

 of the corpus from which the processus Ungualis has developed. 

 The two antero-lateral angles of the corpus (processus lateralis 

 anterior) are continuous laterally and posteriorly with the very 

 short cornua hyaha. The processus lateralis intermedius is 

 small and separated from the cornu branchiale primum. The 

 processus lateralis posterior is continuous at this stage with the 

 stout cornu branchiale secundum. The cornua hyaha may be 

 differentiated from the processus lateralis anterior by a deep 

 cleft which extends anteriorly from behind so that the cornu 

 itself is represented by a broad, flat, stump which projects pos- 

 teriorly and is thicker at its distal than at its proximal end. 



The cornua branchialia prima are the longest of all the cornua 

 and are long cyhndrical rods, tapering very gradually toward 

 their distal ends, and curved at first slightly in a postero-lateral 

 direction and then toward their distal ends in simply a dorsal 

 one. At their extreme distal ends they bend sharply in a medial 

 direction and anteriorly to form short hooks whose free ends are 

 directed forwards. These rods are in close relationship to, but 

 are not continuous with, the processes of the corpus by their 

 proximal ends. The cornua branchialia secunda are at this 

 stage continuous with the processus laterales posteriores. They 

 are heavy rods of ellipitical cross section, rather thicker than the 

 cornua branchialia prima. They are parallel in general with the 

 last mentioned and terminate with their distal ends slightly 

 upturned some distance ventral and medial to the extremity of 

 the cornu branchiale primum. The second pair of cornua are 

 considerably shorter than the first and so do not extend so far 

 posteriorly. 



No trace of an entoglossum occurs in the embryo modelled, 

 but in an older individual (carapace length, 28 mm.) I find a 

 thin plate of cartilage just ventral to the anterior end of the cor- 

 pus hyale. It extends beyond the processus lingualis and is sep- 

 arated from it by only a thin layer of connective tissue. It is 



