EOSIREN LTETOA. 
190 
edges make an angle of about 100° with one another. The foramen magnum (/’m.) 
itself is wider than high; its upper margin is deeply notched in the middle line, on 
either side of which the cxoccipitals arc produced into low tuberosities which overhang 
the opening. Laterally the exoccipitals are produced downwards into paroccipital 
processes, which resemble those found in the Uugong 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 squamosal?. The sui)raoccii)ital 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 hy 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-flgure 04. 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 premaxilloe, which form the whole of the 
side and front border of the uarial 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, llalitherium scliinzi, 
pp. 64-06 *.) 
The maxilla [mx.) is a very large bone with a great antero-posterior extensioii. 
■* Abbiindl. d. Mittelrbeiuischen geol. Vereins, vol. i. pt. 1 (Darmstadt, 1881). 
