. Bulletin of the British Museum (Natural History), Geology. 49^ MEGISTOTHERIUM FROM laterally against the supraoccipital. Although the crest forms a vertical plate of bone, it is not quite flat; the distinct kinks could reflect slight differences in develop- ment of temporal muscle on left and right sides, or may be due to postmortem changes—the skull was fossilized with the dorsal surface lacing downwards. The crest carries on the right side a large nutrient foramen. Occipital. Viewed posteriorly the skull presents a trefoil pattern, formed of supraoccipital and two exoccipitals. The supraoc
. Bulletin of the British Museum (Natural History), Geology. 49^ MEGISTOTHERIUM FROM laterally against the supraoccipital. Although the crest forms a vertical plate of bone, it is not quite flat; the distinct kinks could reflect slight differences in develop- ment of temporal muscle on left and right sides, or may be due to postmortem changes—the skull was fossilized with the dorsal surface lacing downwards. The crest carries on the right side a large nutrient foramen. Occipital. Viewed posteriorly the skull presents a trefoil pattern, formed of supraoccipital and two exoccipitals. The supraoccipital, broken dorsally, is sphenoidal, narrowing toward the foramen magnum. A pair of very large pits occupying most of the supraoccipitals witness the enormous rectus capitis musculat- ture. Immediately below these are two very large nutrient foramina which pass ventrally to a common opening on the roof of the foramen magnum. The exoccipital is dominated by the wide and massive paraccipital process; no separate mastoid process can be distinguished. The heavy paroccipitals must have carried heavy rectus capitis anterior and lateralis muscles for lateral head movements. The foramen magnum is roughly circular in outline and about 3 -5 cm in diameter; on its inner margin it carries dorsally an opening which communicates with the two nutrient foramina on the supraoccipital. On the internolateral border can be seen the posterior lacerate foramen which passes anteriorly to open in the ear region. On the ventrolateral border is a further opening from the foramen magnum to the basioccipital, with a passage leading toward the ear region. The occipital condyles are large ovoidal facets, strongly keeled, with long axis directed ventromedially; the condyles almost meet ventrally with only a shallow notch separating them. The basioccipital is a relatively thin bridge of bone between the exoccipitals and the massive basisphenoid; the paired anterior condyloid foramen is clearly
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