28 DINOCEUATA. 



bone is swollen by this socket, so as to present, in tlie males at least, a 

 prominent rounded ridge on the side of the face. The alveoli for the pre- 

 molar and molar series of teeth are similar to each other, eacli presenting 

 three pits for the reception of roots, aIz : an iinier large pit, and two outer 

 small ones. Over these, the bone is thin, as is usual on the buccal surface 

 of the maxillary. 



Behind and above the jjosterior molar teeth, in the orbital .region of 

 the skull, tlie maxillar}- bone presents several fissures, or foramina, close 

 to, or in, the suture with the palatine. The first of tliese may be indistinct, 

 or of different shape on the opposite sides, and is just back of the last 

 molar, as shown in the skull of Blnoceras Incase, on Plate IX, figure 2. 

 In Diuoceras mirdhUf (number lOoG), three such fissures are situated on the 

 right side of the skull, in or near the maxillo-jialatine suture, back of the 

 orbit. One or more of these apertures ajipear to be the posterior openings 

 of the posterior jjalatine foramina, an arrangement similar to that seen in 

 the hippopotanms. 



The Palatine Bones. 



The palatine bones form only a small part of tlie bony" palate in 

 Bliiocerns. The palato-maxillary suture in Diiwccras mirahile (number 

 1036) is nearly opposite the middle of the second molar, and about 20"'™ 

 in front of the i)osterior border of the bony palate, (Plate V). It is at first 

 nearly transverse to the palate, then runs l)ackward around the last molar, 

 and turns upward into the orbital region, where it cannot be followed with 

 certainty. Posteriorly, the palatine is in contact with the pterygoid, and 

 the pterygoid plate of the alisphenoid. On the median line of the palate, 

 the suture between the opposite palatines is obliterated. 



The palatines continue the lateral walls of the posterior nasal cavities 

 considerably behind the last molar, and these walls are still further 

 extended In' the ])terygoid bones. 



