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The ventro-posterior limb of the supraoccipital extends ventrally almost to the dorsal margin 

 of the foramen magnum, being separated from that margin by a median bit of cartilage. This exposed 

 bit of cartilage forms the hind end of a median band which separates the dorsal edges of the exocci- 

 pitals. The postero-lateral edge of the skull, the edge that separates its posterior and lateral surfaces, 

 is thin, and projects ventro-laterally as a tall ridge. The ventral portion of this edge is formed by 

 the exoccipital and lies in a nearly horizontal position; its dorsal portion, formed by the posterior 

 process of the pterotic, lying in a nearly vertical position. Between these two portions there is a 

 large rounded corner formed by the opisthotic. This gives to the posterior surface of the skull a 

 flattened hexagonal aj^pearance. 



The temporal fossa is small and shallow, and on one side of one of the three specimens examined 

 was almost obliterated by the encroaching growth of the bounding bones. The anterior portion of 

 the fossa was especially affected by this contraction, but still remained as a small recess roofed by 

 the small lateral extrascapular. 



The dorsal surface of the skull is formed, as in Trigia, by the nasals, mesethmoid, ectethmoids, 

 frontals, postfrontals, sphenotics, pterotics, parieto-extrascapulars, lateral extrascapulars and supra- 

 scapulars. All of these bones come to the level of the outer surface of the skull, the exposed portions 

 of all of them being similarly marked by surface granulations. Slightly grooved lines mark most of 

 their contours. Anterior to the nasals, and lying at a but slightly lower level, there is a small rostral 

 depression. The floor of this depression is formed in part by a narrow, thin and smooth projecting 

 plate of the deeper layers of either nasal, in part by the ascending processes of the vomer, and in 

 part by a small intervening portion of the cartilage of the rostrum. The mesethmoid is entirely 

 shut off, by the nasals, from bounding relations to the depression. 



The MESETHMOID has an exposed dorsal surface that is usually somewhat lenticular in 

 shape, and the stout, median, mesethmoid spine rises from it, slightly anterior to its middle point. 

 Beneath the superficial, dermo-perichondrial portion of the bone there is a primary portion, of less 

 extensive surface, which extends completely through the cartilage of the snout. In its deeper portion 

 this primary component expands, and becomes a circular plate formed around a point that lies directly 

 beneath the median mesethmoid spine. Between this circular basal plate of the bone and the dorsal 

 dermo-perichondrial plate, there is, on the lateral and posterior edges of the bone, a deep groove; 

 the grooves on the lateral surfaces of the bone being exposed laterally, but the one on the posterior 

 surface lying within the cartilage of the skull. The lateral edge of the dermo-perichondrial component 

 of the bone suturates w-ith the mesial edge of the corresponding component of the ectethmoid, a canal, 

 large anteriorly but small posteriorly, being left between the two bones; the canal lying parth^ be- 

 tween the primary components and partly between the deeper layers of the dermo-perichondrial 

 components of the bones. The smaller, posterior portion of this canal transmits the supraorbital 

 latero-sensory canal and the ramus ophthalmicus superficialis; the larger anterior portion trans- 

 mitting that same canal and nerve, and also the nervus olfactorius. A varying number of openings, 

 between the ethmoid bones, lead from the canal to the outer surface of the skull, but they are all 

 closed externally by membrane. Anteriorly the mesethmoid suturates with the nasal bones, and 

 posteriorly with the frontals. Ventrally, its primary portion lies directly upon the dorsal surface 

 of the parasphenoid, the two bones being so firmly attached to each other that they would seem 

 to be in process of ankylosis. 



