>o. 2118. EXTINCT SIRENIAN DEHM0)ST¥LU8 HESPERUS— HAY. 389 



The lachrymal (pis. 56, 58, 7) is a very considerable bone in Des- 

 mostylus. It does not appear on the face, as in the Ungulata, but it 

 forms the inner wall and the roof of the orbit. The position is as in 

 the elephant, but the bone is far more developed than in the elephant. 

 The sutures bounding its hinder half are not as distinct as desirable, 

 but the length from the front to the rear is at least 50 mm. Over 

 the orbit it forms the supraorbital process, but it is here covered 

 over by the frontal. In the specimen described the frontal on the 

 right side has been split off from the process so as to expose the part 

 belonging to the lachrymal. This bone does not come into contact 

 with the suborbital process of the malar, as it does in Halicore, but 

 there intervenes between them a narrow strip of the maxilla. The 

 lachrymal is imperforate. 



The maxUlae have lost a part of their anterior ends. In Yoshiwara 

 and Iwasaki's figures these bones are represented as coming forward 

 as far as the front of the nasal opening ; hence in our specimen prob- 

 ably about 50 mm. of each bone is missing at the side of the snout. 

 On the palatal surface, near the midline, is seen a fragment of the 

 premaxiUa and the premaxillo-maxiUary suture. From this suture 

 to the hinder end of the maxilla is a distance of 180 mm. In front 

 of the orbit it rises to join the nasal for a distance of about 18 mm. 

 Anteriorly this nasal process joins the premaxiUa; posteriorly the 

 frontal and lachrymal. At the front of the orbit the maxiUa passes 

 beneath the anterior process of the malar. Just how it ends at the 

 anterior end of the zygomatic arch is not clear, inasmuch as the 

 bone is injured here on both sides. On the underside of the arch, 

 below the rear of the orbit, there appears to have been a downwardly 

 directed process, similar to that which is seen in Halicore and Tri- 

 chechus, descending from the lower border of the malar. The dimen- 

 sions of this process can not be determined exactly, except that here 

 the bone is about 5.5 mm. thick. 



Beneath the shelf of bone under the orbit, formed by the malar 

 and the maxiUa, the bone is conspicuously excavated. Vertically 

 the excavation reaches from the side of the snout to the alveolar 

 border of the jaw; fore and aft, from the side of the snout to below 

 the rear of the orbit. In the bottom of this excavation opens the 

 infraorbital foramen. Seen from below, the maxillae meet in the mid- 

 line by a straight suture along a low ridge ; and they extend backward 

 to join the palatines, as has been described. The palate along these 

 bones is concave longitudinally as well as transversely. At the rear, 

 at some distance in front of the palatine suture, is a pair of openings, 

 the post-palatine foramina. The alveolar border on each side is 

 narrow in front, but about half way back to the palatine border it 

 begins to widen, to accommodate the teeth. At the rear this border 

 is bounded inwardly by a strong ridge which articulates with the 

 palatine. 



