the Skull of Dijulcmodoii. 311 



The postfrontal sends a process bacUwartls alonoj the 

 outer face of tlie parietal and vcntrally bears a coiitinnatioii 

 of this process, wliieii in elfeet continues the brain-ease and 

 no doubt gives protection to the olfactory nerves. The 

 suture separating the postfrontal from the jngal cannot be 

 seen. 



Prefrontal (tigs. 1 & 2). — The prefrontal is a large bone 

 forming about one-quarter of the orbital margin ; it unites 

 by sutures with the |)ostfrontal, frontal, nasal, and lachrymal. 

 It has a powerful orbital plate, forming part of the front 

 wall of the orbit and uniting with the corresponding plate of 

 the lachrymal ; this plate also reaches down to touch the 

 nj)\vardly directed process of the maxilla or palatine. 



Lachrymal (fig. 2). — The lachrymal is a smaller bone than 

 the prefrontal; it forms the front of the orbit and sends a 

 long orI)ital ramus back over the dorsal surface of the 

 palatal process of the jugal, so as to form a good deal of the 

 floor of the orbit. 



The lachrymal bears two small grooves leading over the 

 rim of the orbit^ which are separated by a low ronnded 

 process with a rough summit. Low down on the facial part 

 of the bone is a lachrymal foramen of moderate size, and 

 within the orbit in the orbital plate two more small 

 foramina. 



Nasals (fig. 1). — The remaining parts of the nasals show 

 nothing of interest ; they broaden posteriorly and unite with 

 the frontals, prefrontals, lachrymals, and maxilliic. 



There still remains to be considered a remarkable bone 

 exposed only in transverse section on the broken end of the 

 snout. As seen here it is a single median bone of oval 

 section, narrow from side to side and standing close above 

 the secondary plates of the maxilla, but not in contact with 

 them. 



1 shall discuss this bone further in connection with other 

 specimens. 



Description of part of a, Loirer Jam ivlrich prohahly helovps 

 to the same, individual as the Skull described above. 



R. 3588 is a fragment of the anterior part of the lower 

 jaw of a Diademodon which is preserved in the same rather 

 unusual matrix as the skull 1 have described above, and 



21* 



