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Show 80 ZOOLOGY OF TilE VOYAGE OF TIIE BEAGLE. d f bove the upper e<lg·e of the petrous bone, 'd · d bl' ely upwar s rom a n gc contmue o Jqu . t d holly behind the cerebrum ; we learn also that the cerebellum has been SJtua e w . _ . f th endm·incr parts that these penshable mas:ses we1e not from the same structure o e b . . . b t 1m but by a membraneous tentorium, as In divided as in the Mams, by a ony sep t ' • k d ' . d'll , . the Orycteropus as has been before remar e , the Glossothere and At rna 1 os. m • . . · . b . :d extending into each side of the tentonum. there IS a strong, shmp, ony n ge 1 1 t f The vertical diameter of the cerebellum and medulla obl?ngata equa 8 t la 0 l b d · t ·ncbes t)1ree Jines· the transverse diameter of the cerebel-t 1e cere rum, an IS wo 1 • . · h lum was about three inches nine lines; its antero-posteriOr ext~nt ab~ut one me and a half. The sculpturing of the internal surface of the cran1al cavity bes~eaks the high vascularity of the soft parts which it contained, and there _are ev1~ent indications that the upper and lateral surfaces of the brain had ?een d1spo~ed m a few simple parallel longitudinal convolutions. ~he two antenor ~ondylotd for~mina( m) have the same relative position _as the smgle_ correspondmg ~oramen m the Glossothere, Orycterope, and Armadtllos, and the mner surface of the skull slo es outwards from these foramina to the inner margin of the occipital condyle. p Of the bones of the face there remain only portions of the malar, lachrymal, palatine, and maxillaries. The chief peculiarities of ~he malar b~ne have bee_n already noticed: the breadth of the base of the descendmg massetenc processe~ 1s two inches two lines; its termination is broken off: the length of the ascendmg post-orbital process of the malar cannot be determined from the same cause, but it is fortunate that sufficient of this part of the cranium should have been preserved to give this evidence of the affinities of the Scelidothere to the Megathere. The malar bone is continued anteriorly, in a regular curve forwards and upwards, to the lachrymal bone, and completes, with it, the anterior boundary of the orbit: the size of the orbit is relatively smaller than in the Orycteropc, and still less than in the Ant-eaters: here, however, we have merely an exemplification of the general law which regulates the relative size of the eye to the body in the mammalia. The malar bone does not extend so far forwards in front of the orbit as in either the Orycterope or Armadillo; in the inclination, however, with which the sides of the face converge forwards from the orbits, the Scclidothere holds an intermediate place between the Armadillos and Orycterope. The lachrymal bone does not extend so far upon the face in the Scelidothere as in the Orycterope; in which respect the Scelidothere resembles more the Megathere. The foramen for the exit of the infra-orbital nerve has the same situation near the orbit as in the Megathere; its absolute distance from the anterior border of the orbit is only half that in the Orycterope. The foramen is single in the Scelidothcre, as in the Orycterope; in the Mega there there are two or three antorbital foramina. The vertical diameter of this foramen is eight lines, the transverse diameter four lines. So much of the outer surface of the superior maxillary bones as has been pre- FOS IL MAMMALIA. 81 served, is smooth and vertical. Each superior maxillary bone contains the sockets of five teeth, occupying an antero-posterior extent of three inches seven lines, (Pl. XXII _and XXIII: fig. 3). The posterior alveolus is situated just behind the transverse lme, extendmg a~ross the an.terior boundary of the orbits ; the remaining sockets of the molar senes extend forwards three inches in front of the orbits. Jn the Megatherium, the roots of the five superior molars are all situated behind the anterior boun~ary of the orbit: in the Orycteropus, on the contrary, the grinders are a11 placed m advance of the orbit; so that the Scelidothere resembles that species more than the Megathere in the relative location of the teeth. The palatal inter-pace between the roots of the last molar tooth of each series is eleven lines; the palat~ gradually thong? slightly widens, as it advances forwards: the posterior margm of the palate IS terminated by an acute-angled notch. In the breadth of the bony palate the Scelidothere is intermediate between the Megathere and Orycterope. The anterior of the upper molars is represented at fig. 3, 4, and 5, Pl. XXI., and at 1, fig. 3, Pl. X XIII.; it corresponds closely in form and size with the opposite molar below ; the base of the triangle given by its transverse section is turned inwards and obliquely forwards. The second molar of the upper jaw, also presents in transverse section a triangular form, with the angles rounded off; but the inner side of the tooth is traversed by a longitudinal gi'Oove. The largest diameter of the transverse sectiou, which is placed obliquely as regards the axis of the skull, measures ten lines and a half; the opposite diameter of the tooth is six lines. The third ~nd fourth molars present the same form and size, and relative position as the second. . The fifth molar is the smallest of the series; its transverse section gives an mcquilateral triangle, with the corners rounded off; the broadest side is turned outwards, and is slightly concave ; the antero-posterior diameter of tlJis tooth ~s se_ven lines; the tmnsverse four lines. The length of the teeth in the upper Jaw IS about two inches and a half. It is almost superfluous to observe that the teeth of the Scelidothere as in other Brnta, are without fangs, and have their inserted base excavated by large conical cavities, for the lodgment of a persistent pulp. The tooth is composed of a small central body of coarse ivory or 'dentine,' traversed by medullary canals, which at the periphery of the coarse dentine anastomose by loops, from the convexity of which the calcigerous tubes are given off which form the fine dentine: the layer of this substance, which immediately surrounds the coarse dentine, is about one line and a half in thickness, and the whole is invested with a very thin coating of cement. The teeth of the Scclidothere thus M |