DEVELOPMENT OF THE SKULL OF EMYS 749 



portion of the maxillare becomes somewhat tw'sted at the ante- 

 rior end where the bone embraces the olfactory capsule so that 

 the dorsal surface becomes strongly inclined toward the median 

 plane of the head. There may be distinguished three definite re- 

 gions, the processus palatinus, processus alveolaris, and processus 

 praefrontalis. The processus palatinus is horizontal, exhibiting a 

 dorsal and a ventral surface; it is of nearly uniform thickness 

 throughout, but becomes slightly thicker at the anterior than 

 at the posterior end. Near its posterior end it is perforated 

 by a small foramen for the ramus maxillaris nervi trigemini, 

 which passes from above tlirough the foramen to continue 

 forward on the ventral side of the maxillare, lateral to the pro- 

 cessus alveolaris. This latter has a vertical position, spring- 

 ing from the mid-ventral line of the processus palatinus and 

 increasing in height from posterior to anterior. For the ante- 

 rior one-third of its length the maxillare is made up entirely of 

 the processus praefrontalis which is continuous ventrally with 

 the anterior end of the processus alveolaris and dorsally with 

 the processus palatinus. At the junction of the processus pala- 

 tinus and praefrontaUs are several irregular foramina (foramina 

 alveolaria externa superiora.) 



The processus praefrontalis has a concave median and convex 

 lateral sm-face and embraces the posterior two-thirds of the 

 olfactory capsule ventro-laterally. Its antero-median margin is 

 hollowed slightly in order to acconimodate the praemaxillare. 

 The dorsal margin of the processus praefrontalis Ues in the same 

 plane with and rather close to the ventral margin of the prae- 

 frontalis. 



The processus palatinus is overlapped dorsally for a very short 

 distance by the anterior end of the zygomaticum so that the 

 two bones together complete the margin of the orbit posteri- 

 orly and ventrally. It lies in the same horizontal plane with 

 the' palatinum which comes to he in close relation to it by its 

 anterior end. 



The praemaxillare (prm.) is of small irregular form situated 

 ventral to the olfactory capsule in the region of the foramen prae- 

 palatinum and medial to the anterior end of the maxillare. Like 



