264 G. T. BETTANY ON THE GENUS MERYC0CHO3RUS. 



with the posterior border of the orbit, and the anterior angle being 

 undefined, as the surface is continued by the nasal bones. The 

 frontal surface is generally somewhat convex; but it is slightly 

 concave behind, in the angle between the two temporal ridges, and 

 also in front of the supraorbital foramina, which are about three 

 quarters of an inch distant from one another, on a level rather 

 behind the middle of the orbit, and about half an inch in front of 

 the median point to which the nasal bones converge. From each 

 foramen a groove, more or less marked in different species, runs 

 forward and is gradually lost on the nasal bones. 



The upper surface of the face is elongated and comparatively nar- 

 row. It is constituted entirely by the nasal bones, which do not 

 extend downwards on the side of the face. Each nasal bone is 

 slightly convex transversely ; and the two together form a very 

 regular convexity, which is greater or less in different species. 

 Posteriorly the outer margins of the two nasals converge gently to 

 a point in the middle line. Anteriorly they together form a pro- 

 jecting triangle, which is thickened below at the apex ; this latter 

 overhangs the nasal aperture, but does not extend quite so far 

 forward as to overhang the extremity of the prsemaxillse. 



The upper part of the nasal aperture is almost square ; but infe- 

 riorly it is produced to an angle of 30°, ending in a rounded form as 

 a notch between the diverging premaxillary bones, which are 

 anchylosed at the alveolar border and for about half an inch above 

 it. The inner margin of each praemaxilla bounds the nasal aperture 

 entirely in rather more than its lower half; the maxillary bone 

 bounds it at its widest upper part, while the nasals complete the 

 boundary above. 



The lateral aspect of the face is nearly oblong, and almost vertical ; 

 and its height is, within a little, equal to its length. The posterior 

 part of the face is not more than three quarters of an inch higher 

 than the anterior. The facial surface presents, in front of the 

 orbits, the following inequalities. First, the lachrymal fossae, just 

 in front of the middle of the inner boundary of the orbit. This 

 fossa may vary from comparative shallowness to considerable depth, 

 and from a rounded to a nearly conical shape. Secondly, the gently 

 convex continuation of the lower part of the zygoma on to the face, 

 graduating above into the lachrymal fossa, in front into the vertical 

 and flat anterior part of the face, and below into the depression 

 above the premolar teeth. Thirdly, the latter depression, more 

 marked anteriorly than posteriorly, and containing just below the 

 anterior termination of the zygomatic ridge the infraorbital fora- 

 men, a vertically-placed oval opening directed forwards ; its position 

 varies, as also does the depth of the fossa. Fourthly, a rounded 

 convexity corresponding to the fang of the upper canine tooth, 

 forming the extreme external part of the front of the face. Be- 

 tween this prominence and the upper vertical part of the side face, 

 an oblique groove, which probably served to convey a nerve to the 

 upper lip, passes downwards to the front of the praBmaxilla. 



Unfortunately I have to describe the zygoma and its posterior 



