156 BRITISH FOSSIL REPTILES. 



gradually decrease in size to a diameter of half an inch. The form of the alveolar 

 aperture is, for the most part, a full oval, nearly circular, with the long diameter 

 inclining more or less transversely. 



The margins of the larger maxillary alveoli are the most prominent. The 

 entire alveolar series describes longitudinally and horizontally a gently undulated 

 course, the premaxillary series forming a slight convexity, and the larger maxillary 

 alveoli a similar convexity, outward. Longitudinally and vertically the alveolar 

 border is almost straight as far as the seventeenth tooth, and then gently bends 

 upwards to the hind end of the series. A groove, deepening into fossas answering 

 in number to the alveoli, extends along the inner side of each premaxillary series. 

 This groove is interrupted at the diastema between the premaxillary and maxillary 

 alveoli : it recommences at the inner side of the maxillary series, also deepening 

 into pits opposite the inner and back part of the alveoli, and continues, though 

 feebly indicated, along the hinder third of the alveolar series. 



The bony palate is entire, save at the palato-nares (ib., fig. 2, r, r) ; but on the 

 inner side of the twelfth socket, counting backward, on each side, there is a nervo- 

 vascular foramen terminating a canal in the upper jaw, directed obliquely down- 

 ward and forward : the foramen is elliptical, an inch in diameter ; a shallow 

 channel extends a few inches in advance of its outlet, and three or four similar 

 but smaller foramina succeed each other anteriorly near the inner wall of the 

 internal alveolar groove, leading to a linear channel 7 inches long, which, with its 

 fellow on the opposite side, defines the base of a median longitudinal ridge of the 

 bony palate between the first three pairs of maxillary alveoli, which ridge 

 is transversely convex, and about an inch in breadth. As the bony palate 

 expands in breadth, behind the nervo-vascular foramina, it presents trans- 

 versely a broader median convexity, bounded by lateral shallow concavities. On 

 the transverse line, between the sixteenth pair of alveoli, are the anterior 

 ends of the palatine bones, which are divided by a median suture (20, 20). 

 The major part of the palato-nares are bounded by the pterygoids (21, 24), 

 which extend backward to the base of the occipital condyle, underlapping 

 the basi-sphenoid and basi-occipital, developing ridges which project below the 

 level of the lateral parts of the fossa, and converging to meet behind the area, 

 including the posterior nostrils. External to these ridges the pterygoids diverge 

 to abut against the tympanic pedicles.^ The mesial border of an ectopterygoid is 

 preserved at 25, fig. 1 . 



The number of alveoli in each ramus of the mandible (PI. 19, fig. 1) is twenty- 

 five or twenty-six. The five alveoli corresponding with the premaxillary sockets 

 in the upper jaw are the largest. They are separated by similar intervals. 



' The tympanic articulations of the lower jaw, which extend the cranium beyond the condyle, are 

 broken off. 



