Mr. T. Attliej on Antliracosaurus Russelli. 149 



The floors of the orbital vacuities being deficient, they appear 

 like two perforations of the cranium, the inner side of the left 

 and the outer side of the right one having portions of bone only 

 partially filling them up (Plate VIII. fig. 1, 0. F) . These por- 

 tions are parts broken off" from the pterygoid bones, which, as 

 can best be seen on the under surface of the skull (Plate IX. 

 O.V), formed originally the floors of the orbital vacuities. 



The parietal foramen is distinct ; and the channels leading 

 to the external auditory openings are also well defined, espe- 

 cially on the left side. 



The premaxillaries are very strong bones, but of small size, 

 measuring from front to back, on the median line, on which 

 they are firmly united, only 1 inch. Their anterior borders, 

 slightly arched, form the rounded snout. From side to side, 

 along their anterior margins, they measure 3 inches. On each 

 side they articulate behind with a small part of the maxilla, 

 and form the anterior concave border of the nasal orifices. 

 Between these parts they are bounded entirely by the nasal 

 bones, indenting them deeply on each side of the middle line. 



The maxillaries occupy the margins of the upper jaw be- 

 hind the premaxillaries, and are very long (11| inches), very 

 narrow, and of small vertical extent. They articulate with 

 the premaxillaries in front, and form the outer posterior mar- 

 gins of the nasal orifices. Their inner margins articulate 

 anteriorly for a short distance with the nasals, then for 

 3 inches with the lacrymals, afterwards for 6| inches with 

 the jugals, and, lastly, by | inch posteriorly with the quadrate- 

 jugals. 



The nasals lie immediately behind the premaxillaries and 

 before the frontals ; they are much broader in front than 

 behind, and occupy the whole space between the nasal orifices, 

 of which they close the inner and posterior margins ; they are 

 bounded on their outer sides by the maxillaries for an inch, 

 and next by the lacrymals for fom- inches. 



The lacrymals are of an elongated pear-shape, the point in 

 front, occupying the angles left by the maxillaries and nasals. 

 They are bounded by the nasals internally, by the prefrontals 

 posteriorly, and by the maxillaries and jugals externally. 

 They do not enter into the formation of the orbital vacui- 

 ties (as in Loxomma) ; the prefrontals intervene, separating 

 them by a considerable space from those vacuities, and forming 

 nearly the whole of the anterior borders of the latter. 



The frontals, a little longer and narrower than the nasals, 

 are broader before than behind, united in front to the nasals, 

 behind to the parietals, and, by the straight median suture, to 

 each other. Their outer margins are articulated to the prc- 



Ann. & Mag. N. Hist. Ser. 4. FbZ. xviii. 11 



