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Show 60 ZOOLOGY OF TilE VOYAGE OF TilE BEAGLE. Glossotheriwn, in forming part of the circumference of an ellipse, whose lo~g axis is vertical; and in sending outwards, from its anterior part, a convex emmence, which terminates in a point directed downwards and forwar?s. . Such appear to be the most characteristic features ~f the cramal fr~gment un rl er cons1' d era t'w n, 1· n w h1' c h we have c1'0 und , that the artlcular s•u rfac• e •f m the os byoides throws more light upon the nature of the animal of whJCh . It IS a part, than even the glenoid cavity itself. There now remains to be ~escl'lbed .a~ much of the individual characters of the constituent bones as the speetmen exlub.Its .. The occipital bone, besides forming the posterior and part .of the mfenor parietes of the cranium, extends for about Lal.f an inch u~on the s1des,. where the ex-occipital element is articulated by a vertical suture wtth the mastotd element of the temporal: this suture is situated in a deep and well-marked muscular ?epre~sion (e, fig. 1), measuring three inches in the vertical, and upwards of one ~n~h. m the transverse direction. The other sutures, uniting the occipital to the adJommg bones, are obliterated. The breadth of the occipital region must have exceeded the heirrht of the same by about one-third. The condyle extends nearly to the external boundary of the occipital aspect of the cranium; there is situated, external to it, only a small ovate, rounded and smooth protuberance. The slightly concave surface of the occipital plane of the cranium is bounded above by a thick obtuse ridge, the muscular impressions are well sculptured upon it. It is traversed transversely at its npper third by a slightly elevated bony crest; and the surface below this ridge is again divided by a narrower intermuscular crest, which runs nearly vertically, at about an inch and a half from the external boundary of the occipital plane. As a similar crest must have existed on the opposite side, the general character of the occipital surface in the Glossothere would resemble that of the Toxodon. A similar correspondence may Le noticed in the terminal position of the condyle, and the slope of the occipital plane. Above the transverse ridge, the rough surface of the occipital plane slopes forward, at a less obtuse angle with the basal plane, to the first named ridge which eparates the occipital from the coronal or superior surface of the skull. The contour of this surface runs forwards, as far as the fragment extends, in an almost traight line : the extent of snrface between the temporal muscular ridges must have been about five inches posteriorly, but it decreases gradually as it extend forwards: all that part which is preserved is quite smooth. The attachment of the fasciculi of the temporal muscle, and the convergence of their fibres as they passed through the zygoma are well marked on the sculptured surface of the bone. The zygomatic process is relatively stouter than in Orycte- 1'opus: it is prismatic: the external facet is nearly plane: the superior is concave, and increases in breadth anteriorly: the inferior surface offers a slight convexity behind the flattened articular surface for the lower jaw. The margin FOS IL .MAl\Uf ALIA. Gl of the zygoma formed by the meeting of the upper and lower facets presents a semicircular curve, extentleu transversely from the cranium, anu directed forwards. The anterior extremity is obliquely truncated from below upwards and fo~·wards, nnd presents a flattened triangular surface indicative of its junction w1th an os malre: the space between this extremity and the side of the cranium measures one inch and nine lines across, and thus gives us the thickness of the tempo~·al mu~cle. The distance from the origin of the zygoma to the occipital plane ·~ r~lattvely greater than in Oryc/.eropus; Glossotlteriurn is in this respect more sumlar to My1·rnecopltaga and Llilanis. The sphenoid bone forms a somewhat smooth protuberance below and behind ~he base of the zygoma. The tympanic bone is wedged in between this protuberance m fro~1t,. anu the mastoid process behind. The chief peculiarity of the broad mastoid 1s the regular semicircular cavity at its under part for the articulation of the styloid bone of the tongue. This depression is separated below by a ?r~ad rou.gh protuberance from the foramen j ugulare, U. fig. 2, Pl. XVI,) which IS n~medwtely external to, and slightly in advance of the great foramen condyloldeum, c . . A small l'Llg?'ed portion of the os petrosum separates the jugular from the carottu canal, wluch arches upwards and uirectly inwards to the side of the shallow sella turcica, (the external and internal orifices of the carotid canal are shown at g, figs. 2 and 3). The chief protuberance on the basis cranii is a large and r~gged one, serving fot· the attachment of muscles, and due chiefly to ~he expansiOn of a great sinus in the body of the sphenoid. This protuberance IS separated from the smaller sphenoid protuberance before mentioned by a large groove continued downwards and forwards from the tympanic cavity, and containing the Eustachian tube, which does not traverse a complete osseous canal. Immediately internal to the glenoid cavity is the large orifice of tlte canal transmitting the third division of the fifth pair of nerves, the principal branch of which endows the tongue with sensibility; this foramen (It, fig. 2) is rather less than tlJat for the muscular nerve of the tongue. The internal surface of the present cranial fragment affords a very satisfactory idea of the size all<] shape of the brain of the extinct species to which it belongs. It is evident that, a in other Bruta, the cerebellum must have been almo t entirely exposed behind the cerebrum; and that the latter was of small relative size, not exceeding tllat of the Ass; and chiefly remarkable, as in the Orycterope, Ant-eater, and Armadillo for the great development of the olfactory ganglia. The antero-posterior extent of the cribriform plate, as exposed in this fra gment, is three inches, and the complication of the cethmoid olfactol'y lamella> wl1ich radiate from it into the nasal cavity is equal to that which exists in the smaller Edentata (fig. 3, Pl. XVI). The nasal cavity is complicated in Glosso- |
