208 DESCRIPTION OF A SPECDIEN 



the internal pterygoid plate is separated from the inferior portion of the bone by a longi- 

 tudinal groove. The jjlates meet anteriorly at an acute angle under cover of the palatal. 

 They enclose a deep cavity -which is bounded below by the hamular process, 4 1-2 inches 

 in length and pointing backward and outward. It assists to form a deep notch with the 

 posterior edge of the external plate. The length of the pterygoid process from the outer 

 opening of the foramen ovale is 8 1-2 inches. 



The Parietal. — The surface is concave and forms the greater part of the temporal 

 fossa. The superior border is convex upward and outward. Beginning to follow its course 

 from behind, it is first seen between the squamous and the supra-occiptal ; at the upper 

 end of the latter it sends a triangular portion inward between it and the frontal (PI. vi, fig. 

 1 c), which it then begins to overlap. The anterior edge passes backward and downward, 

 turning round the root of the orbital plate. The posterior inferior border is convex and 

 articulates above with the squamous, and lower down with the alisphenoid, from which it 

 is in part separated by the basisphenoid. 



The Basisphenoid. — As there is no suture between this bone and the basioccipital, and 

 as the neighboring parts, with the exception of one petrosal, have been quite undisturbed, 

 no description of it would be possible were it not for a small piece visible in the temporal 

 fossa. This piece has been identified as a portion of the basisphenoid from information de- 

 rived from the works of other observers, for it would be impossible to name it from the 

 little that is seen on the unopened skull. It is about 4 1-2 inches long ; its greatest width 

 Ls 3-4 inch. It is placed nearly horizontally. The posterior end is pretty solid, but the 

 anterior thin and scale -like, and pointing a little downward. It is between the alisphenoid 

 below and the parietal above. In the B. rostrata^ it appears also to touch the squamous, 

 but in this specimen it is separated from it by about three inches. It is remarkably sym- 

 metrical on the two sides. 



The Frontal. — The bones of the two sides are distinct. The portion nearest the me- 

 dian line is in front of the supra-occipital and of an internal prolongation of the parietal. 

 This part extends forward and outward into a number of delicate laminoe, most of which in- 

 terdigitate with those of the frontal process of the superior maxilla, but a few internal ones 

 with those of the intermaxilla. A V-shaped cavity in the median line is formed by the two 

 frontals, with a little ridge in the middle for the nasals. Below this the frontal is bounded 

 by the ethmoid, and on the side overlapped by the parietal. The superior border continues 

 free till it reaches the anterior internal angle of the orbital plate, which is hidden by the 

 superior maxillary. This border is 18 inches long. The surface which it bounds is at first 

 vertical, but soon becomes hoi'izontal, forming the supra-orbital plate (PI. vi, fig. 1 and 2 e). 

 This plate is irregularly quadrilateral. The posterior edge bounding the temporal fossa in 

 front is 22 1-4 inches long, reckoning from the parietal. It is thick, and marked liy two 

 semilunar depressions, of which the internal is much the larger and very rough. The anterior 

 border is of about the same length, and very thin except at its outer end ; it fits more or 

 less accurately into a groove on the upper surface of the maxilla. These two borders con- 

 verge decidedly, as is characteristic of the B. miiscidus ; the anterior is by far the most 

 oblique. The breadth at the base is from 25 to 26 inches ; at the outer edge of the plate 

 it is about 16 inches. This end is very thick ; it is marked behind by a tuberosity where 



'Carte and Macalister, Trans. Royal Soc, 18G7, p. 201. 



