tlie Skull 0/' Diademodon. 311 



The postfrontal sends a process backwards along the 

 outer face of the parietal and ventrally bears a continnation 

 of this process^ wliich in effect continues the brain-case and 

 no doubt gives protection to the olfactory nerves. The 

 suture separating the postfrontal from the jugal 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 tlie postfrontal, 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 

 upwardly 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 orbital 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 rounded 

 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 maxillae. 



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. 



I shall discuss this bone further in connection with other 

 specimens. 



Description of part of a Loiver Jaw which probably belongs 

 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 



