The right maxilla (No. 4) is in precisely the same state of preservation as the specimen just described, and probably belongs to the same skull. Its anterior margin is perfectly preserved, indicating that the facial region is very short in front of the anterior end of the zygomatic arch, which is pierced by a rather large suborbital canal. Its upper border proves that the nasal region was raised into a slightly convex dome; while its antero-superior angle is not rounded as in Mylodon, but curves upwards and forwards and ends in a point as in Grypotherium. At the oral border there are the shattered bases of four teeth.
A fragment of the nasal region (No. 13) may also have belonged to the same skull, but its state of preservation is a little different from that of the two specimens just described. It has clearly been buried in a powdery deposit, which has stained it brown; but the enveloping dust must have been extremely dry, for fragments of cartilage adhere to it, as well preserved as in the nasal chamber of the cranium itself (No. 1). It also bears traces of the integument.
Judging by the figures of the skull of Grypotherium published by Reinhardt (loc. cit.), this specimen seems to have occupied an anterior position in the nasal region. It is thus of great interest, because the three known skulls of Grypotherium leave the precise nature of the bony arcade separating the narial openings undecided. According to Reinhardt, the nasal bones terminate as in Mylodon, and the arcade is an element interposed between them and the premaxillæ. According to Burmeister, the nasals themselves extend forwards and constitute the greater part, if not the whole, of the problematical bar. The fragment now under consideration is clearly in favour of the latter interpretation. Its lower thickened end is a massive bone, not bilaterally symmetrical, and not showing any trace of a median suture. Its inferior face is irregular and roughened, and can scarcely be regarded as an articular facette. Its upper portion consists of a pair of bones separated by a very well-marked median longitudinal suture. These are not thickened at their contracted upper end, where they have evidently been broken, and are not quite bilaterally symmetrical. They doubtless fuse at their lower end with the problematical azygous bone already mentioned, but the arrangement is obscured by the enveloping soft parts. A pair of bones, which may be regarded as nasals, thus extend forwards in a narrow arch to a point just above the anterior end of the premaxillæ; while the massive bone effecting a union between the two normal pairs of elements is probably an ossification in the internasal septum. It is interesting to note that there is an incipient trace of a similar forward production of the nasals in the genus Scelidotherium; while there is sometimes an ossification of the internasal septum in Megatherium.[44]
The three specimens now described, when placed approximately in their natural positions, afford a very satisfactory idea of the form and proportions of the skull when complete. The malar bone is the only important part to be added; but unfortunately it is impossible to decide which of the three specimens of this element in the collection belongs to the individual now under consideration. As already mentioned, these three bones are all different in the shape and proportions of the hinder bifurcated end. They are all very fresh in appearance, but have been stained reddish-brown by the earth in which they must have been buried.
The hinder portion of the second skull already mentioned (No. 2) comprises the occiput and brain-case as far forward as the front of the cerebral hemispheres. It is much battered and broken, and in quite as fresh a state as the cranium already described, with a considerable investment of dried soft parts on its base. It is only very slightly smaller than No. 1, but is of interest as exhibiting some of the sutures, besides a roundness and smoothness indicative of immaturity. The supraoccipital is shown to be very large; a small median point of it enters the foramen magnum, while the suture separating it from the parietals and squamosals extends along the rounded lambdoidal ridge. The horizontally extended suture between the squamosal and parietal on the inner wall of the temporal fossa is seen in the position where Owen determined it to occur in Mylodon.[45] Both tympanics are preserved, but they are more obscured by soft parts than in No. 1.
To this cranium probably belongs a detached portion of the left side of the facial region (No. 5), in a similar state of preservation and slightly smaller than the maxilla (No. 4). The suture between the frontal and the maxilla still persists, while the oral border is preserved farther forward than in the last-mentioned specimen, showing a fragment of the much-reduced premaxilla united with the maxilla by a jagged suture.
The third imperfect occiput is about as large as the immature specimen No. 2, but does not exhibit any features worthy of special note.
The largest and most important portions of the mandible are Nos. 9 and 11, which evidently belong to the right and left rami of one and the same jaw. They are much broken and are in the same fresh condition as the skulls, with traces of the periosteum and even considerable portions of the soft parts of the gum. The right ramus is preserved sufficiently far forwards to show that there was no caniniform tooth in front of the series of four ordinary molars. Judging by the extent of the latter series, the specimen probably belongs to the same individual as the skull No. 1.
Another portion of a mandibular ramus (No. 10) of the left side is slightly smaller than the last and may well have belonged to the immature individual No. 2. It is similarly quite fresh in appearance, and bears the shrivelled remains of the gum. It is interesting as exhibiting the two posterior molars slightly different in shape from those of the former mandible. In this specimen the longer axis of the third molar is oblique, whereas in No. 9 it is coincident with the axis of the mandible; while in the former the fourth molar is not so long in proportion to its width as in the latter. Such slight differences, however, cannot be regarded in the Edentata as more than individual variations.
Brain-cavity and Cerebral Nerves.