58 



skull when found lay on its right side and although very much crushed, certain parts of 

 it supply definite information as to its structure and size. The two orbits, the right 

 maxilla, a quadrate and the occipital condyle were conspicuous and apparently in place, 

 with a large posterior crest extending to the rear. Somewhat in advance of the orbits 

 a horn core, of large size and apparently symmetrical form, occupied a position sugges- 

 tive of a nasal origin, the nasal bones and the frontals being probably represented by the 

 ragraents filling the space between the orbit and the horn core (see fig. 14, from a 

 measured drawing made before the parts of the skull were removed). 



Fia. 14. — Head of Monodonius dawsoni, from a sketch in the tielJ ; uue-twoU'ch the natui-al size, p, parietal ; or, orbit ; 

 oc, occipital condyle ; q, quadrate ; m, maxilla (inner side, showing a row of foramina) ; h, horn core ; s, squaniosal. 



The large posterior crest forms the back part of the skull above ; its exact shape is 

 fortunately supplied by the admirably preserved specimen shown in outline, from beneath, 

 in fig. 15. The surface of the bone, above the orbit and from there inward for a short 

 distance toward the median line of the skull, is moderately smooth and shows no trace of 

 a horn core. 



With the separate posterior crest was found a horn core, similar in shape to, although 

 not as well preserved as, the one belonging to the skull. 



The posterior crest is composed of the parietals and squamosals coalesced. The former 

 are represented by a flat, thin, smooth median portion that expands laterally both in front 

 and behind ; anteriorly it is deeply concave below and broadly convex above but 

 posteriorly it thickens gradually and dividing to either side is continued forward as the 

 squamosals in a broad curve to meet the anterior expansion. On either side of the 

 median element is included a large supratemporal vacuity or fontanelle. 



The posterior crest is somewhat saddle-shaped. Its sides are wavy, with a slight 

 thickening of the bone in the posterior five of the seven corresponding convexities of the 

 periphery, whilst a pair of inwardly directed spurs of bone, with their points turned 

 slightly downward, are developed on its posterior border, one on each side of the median 

 line. The intervacuital element is thickened along its median length and a more decided 

 strengthening of the bone occurs along the posterior border, resembling in this respect 



