EOSIEEN LIBTCA. 199 



edges make an angle of about 160° with one another. The foramen magnum (f.m.) 

 itself is wider than high ; its upper margin is deeply notched in the middle line, on 

 either side of which the exoccipitals are produced into low tuberosities which overhang 

 the opening. Laterally the exoccipitals are produced downwards into paroccipital 

 processes, which resemble those found in the Dugong rather than those of the Manatee. 

 The lower ends of these processes are about on a level with the lower border of the 

 condyles ; their anterior face bears a vertical groove. Superiorly the anterior face of 

 the exoccipital has a broad surface for union with the supraoccipital, and laterally a 

 second for junction with the squamosals. The supraoccipital is roughly hexagonal in 

 outline, the two lower sides uniting with the exoccipitals, between which the lower 

 angle is thrust ; the lateral borders join the squamosals, at least in part, while the 

 upper borders form the middle part of the lambdoidal ridge, being separated in the 

 middle line by a prominence, from which a ridge runs down in the middle line, dividing 

 the surface into two halves, each of which is slightly concave. 



In front of the lambdoidal crest the roof of the cranium formed by the parietals {pa.) 

 is slightly concave both from side to side and from before backwards. In front of this 

 the roof becomes concave from side to side, at least in the middle line, the borders 

 being the somewhat prominent temporal ridges which form the angles between the roof 

 and the nearly vertical sides of the temporal fossse. The narrowest part of the skull- 

 roof is about 6 cm. in front of the lambdoidal crest ; at this point the width is 4'2 cm., 

 but behind this the roof widens slightly to its posterior border, where it measures about 

 5'5 cm. across. Anteriorly it widens out much more considerably, and at the post- 

 orbital processes of the frontals it is 8'8 cm. wide. The sides of the cranium immediately 

 in front of the occipital surface are somewhat rounded, but further forwards are nearly 

 flat and, as already remarked, almost vertical : in this region the bone is thin, while in 

 the middle of the skull-roof the parietals may attain a thickness of 1'8 cm. 



The anterior part of the roof is formed by the frontals (fr.), and the shape of the 

 suture between these bones and the parietals is shown in text-figure 64. Anteriorly 

 they widen out to the large postorbital processes. Their anterior borders are notched by 

 the comparatively large nasals [na.), between which they send a narrow process, which 

 seems to have extended to the nasal opening, thus completely separating the nasals in 

 the middle line. Outside the nasals (see text-fig. 64) the frontals are in contact with 

 the upper ends of the facial processes of the premaxillse, which form the whole of the 

 side and front border of the narial opening. The anterior angles of the nasals seem 

 to be produced downwards along the inner side of the premaxillae till they meet the 

 upper edges of the underlying maxillae. (See also Lepsius, Halitherium schinzi, 

 pp. 64-66 *.) 



The maxilla (mx.) is a very large bone with a great antero-posterior extension. 



* Abhandl. d. Mittelrheinischen geol. Vereins, vol. i. pt. 1 (Darmstadt, 1881). 



