255 



into two large protuberances, one at the part (e) anterior to that supporting the joint 

 for the lower jaw, the other and larger (fig. 2, /) at the angle formed by the down-bending 

 of the arch to the orbital floor ; the latter is most prominent and best defined. The floor 

 of the orbit (ib. fig. 1, r) is of comparatively small extent, limited to the inner or mesial 

 half of the inwardly bent part of the zygoma, of a triangular form, indicative, with the 

 inner orbital concavity leading to the antorbital process (s), of the small relative size and 

 low position of the eyeball ; with this position the foramen opticum corresponds. The 

 extent of the anterior inwardly bent part of the zygoma is 5 inches. From the lower angle 

 of the bend is continued downward the process (21') for an extent of 3 inches, with a twist, 

 making its sides look forward and backward, its borders outward and inward. Its breadth 

 is 2^ inches, its termination subtruncate ; from its inner border to the alveolar part of 

 the maxillary, between the penultimate and antepenultimate molars, is 3 inches 6 lines, 

 giving the span of the arch extending transversely from the anterior root of the zygoma 

 to the masseteric process, the end of which reaches below the level of the upper grinding- 

 teeth (Plate XXXVI. fig. 1, m»). The anterior root of the zygoma is three-sided: one, 

 the upper horizontal surface, forming the floor of the orbit, has a fore-and-aft extent of 

 2 inches ; the anterior and posterior surfaces converge to a thick lower border, which is 

 above the interval between m 1 and m 2, terminating about ] lines above the outlets of 

 the sockets of those teeth. The antorbital foramen (ib. 21) is vertically elliptic, 10 lines 

 in long and 6 in short diameter, situated 1 inch 9 lines in advance of the orbit, and about 

 2 inches above the outlet of the anterior molar (d 3). The antero-posterior extent of the 

 maxillary alveoli, in a straight line, is 7 inches ; their outlets describe a gentle convexity 

 downward as well as outward, the right and left series diverging from the anterior pair 

 to the fourth and incurving slightly at the last pair (Plate XXXVII. fig. 3, ds, ms). 

 The outer roots of the contained molars cause corresponding prominences of the sockets, 

 giving an undulatory surface to that part of the upper jaw (Plate XXXVI. fig. 1). This 

 extends, perhaps in conjunction with the palatine bone, about an inch beyond the last 

 molar, with an upward slope. 



The breadth of the hind part of the palate here is 3 inches 3 lines. The posterior 

 nares form a triangular aperture, with the base above the palate, 2 inches 3 lines broad, 

 thence contracting as it extends obliquely upward and backward to a point at the fore 

 end of the basisphenoid ridge ; the length of the aperture from this point is 4 inches 

 6 lines. The aperture is bounded laterally by the pterygoid plates. 



If, as in the skulls of Mammals generally, we regard the part anterior to the orbits 

 as the facial division, which is often the longest, the corresponding part in Nototherium 

 offers the strangest and most anomalous form and proportions in the mammalian class. 

 It looks like a mere pedunculate appendage to the rest of the skull. Instead of tapering 

 to the end, as is usually the case, it expands forward from its base of attachment both 

 vertically (Plate XXXVI. fig. 1, 15, i 1) and transversely (Plate XXXVII. fig. 2, 15, 22-). 

 The vertical diameter at the base, or from the depression at the root of the nose to tire 

 fore part of the maxillary alveolar process, is 4 inches 9 lines ; the same diameter at the 



