MEG ACEPH ALUS AND P. BRA CIIYCEPII ALUS. 



473 



wards in the middle line and unites by a splintery suture with the 

 palatines behind. It shows traces of a straight sutural union along its 

 median antero-posterior diameter, and consists, without doubt, of the 

 connate vomers. On their outer margin the foramina are bounded 

 (fig. 9) for the anterior three quarters of their extent by the maxillae, 

 for the remaining quarter and along their posterior margin by the 

 palatines, and along the inner border (as before mentioned) by the 

 concave outer margin of the conjoined vomers. The vomero-palatine 



Fig. 9. — Diagram showing the left Internal Naris of P. megacephalus, 

 bounded by the Maxilla, Vomers, and Palatine. (Scale g.) 



suture has more or less the shape of a W, as exposed on the floor 

 of the skull, the apex of the W being on the median line, and 

 the end of its lateral strokes cutting the inner posterior angles of the 

 foramina. 



The palatines extend backwards for some distance as flat, hori- 

 zontal plates, suturally united in the middle line, and completely 

 roofing over the front of the mouth. Their sutural union is inter- 

 rupted for a part of its course by an elongated vacant space (fig. 8,/) 

 which clearly corresponds to the palatal foramen of many Lizards 

 (e. g. Iguana, in which it is well seen). 



An oblique linear fissure starting from the middle of the outer 

 stroke of the W of the vomero-palatine suture runs on each side out- 

 wards and backwards, to disappear against the matrix bounding the 

 roof of the mouth. These fissures might easily be mistaken for 

 sutures, in which case they would be regarded as indicating the line of 

 junction of the palatines; they are, however, simply fractures 

 which have broken the palatines along a line where they become 

 flanged upwards and outwards to join the maxillae. The fractures 

 are, indeed, continued through the skull ; so that the middle part of 

 it, included between them, can be readily separated from the outer 

 part on each side, and the form of the palatines and their union 

 with the maxillae clearly exposed (fig. 10). 



Another fracture traverses the skull nearly vertically, but oblique 

 to the axis, passing through one of the external nares, and one of the 

 oval foramina, or nares, as we may venture to call them, before 

 mentioned. This fracture shows (fig. 11) a large central chamber, 

 now filled with the Lias limestone ; it is bounded above by the 



