. Bulletin of the British Museum (Natural History), Geology. io8 LOWER MIOCENE RUMINANTS Occipital. The dorsal surface of the supraoccipital region is convex as far as the nuchal crest. In the palaeotragines the supraoccipital region is reflected over the condyles but in Prolibytherium it is vertical or slopes slightly anteriorly as in Capreolus. The mastoid process forms the lateral wings of the nuchal crest and the supra- occipital forms the dorsal part of the crest (pi. lo, fig. 2). The medial edge of the mastoid foramen is formed by the occipital bone. On the posterodorsal face of the supr
. Bulletin of the British Museum (Natural History), Geology. io8 LOWER MIOCENE RUMINANTS Occipital. The dorsal surface of the supraoccipital region is convex as far as the nuchal crest. In the palaeotragines the supraoccipital region is reflected over the condyles but in Prolibytherium it is vertical or slopes slightly anteriorly as in Capreolus. The mastoid process forms the lateral wings of the nuchal crest and the supra- occipital forms the dorsal part of the crest (pi. lo, fig. 2). The medial edge of the mastoid foramen is formed by the occipital bone. On the posterodorsal face of the supraoccipital region are paired depressions providing insertion for the semispinalis capitis muscles—the chief extensors of the head and neck. The external occipital protuberance lies medio-ventral to these pits (pi. 10, fig. 2), its surface is deeply sculptured (pi. 10, fig. 2) for attachment of the nuchal ligament. The ventral part of the external occipital protuberance is produced ventrally as a strong median crest. The occipital condyles have sharp keels on their lateral faces (pi. 10, fig. i). The condyles are set very close to the skull; they are relatively large and the bone is. Fig. 4. Dorsal view of the ossicones of Prolibytherium () (One sixth natural size.). a: posterior palmation. b: anterior palmation. c-d: cross-section of the ossicone. e: position of frontal eminence, f: supraorbital groove, g: fronto-nasal suture, h: dorsal opening of supraorbital canal, x-y: cross-section of the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original British Museum (Natural History). London : BM(NH)
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