OCR Text |
Show .53 ZOOLOGY OF TIIE VOYAGE OF THE BEAGLE. ideration. for the lenoid cavity . 1 d t 11 the lower J. aw free motion lS so s lrtpe as o a ow . . h . ' l I g f·otn right to left and forwards OL' backwards, hke the move-m a onzonta p ane, 1 ' • b . b bl ments of a uu.l l-stone; an d , ne"v ei· theless ' I venture to affirm It to e most plw a e, that the food of Glossotlwrium was derived from the animal and not fr?~n t le vcge- table km. gdom; an d to pt.e c1 1' c t , tha~ t when the bones of the extremities sha.l.l be discovered, they will prove the Glos othere to be not an ungulate but an u~guicu-late quadruped, with a fore-foot endowed with the movements. of pronatwn and supm· a t'w n, an d at·med with claws ' adapted to make. a breach. m the stro· nd g wal·l s of the habitations of those insect-societies, upon whJCh there IS good evl ence m other parts of the present cranial fragment, that the animal, though as large as an ox, was adapted to prey. . . . we perceive, in the first place, looking upon the base of ~h1s portwn of skull, a remarkable cavity, situated immediately behind the tympamc bone, of nearly a regular hemispherical form, an inch in diameter (fig. 2, ~· Pl. ~VI ) . Tl~e superficies of this cavity appears not to have been covered with artteular cartilage, for it is irregularly pitted with many deep impressions; and I .conclude, therefore, that it served to afford a ligamentous attachment to the stylotd element of a large os ltyoides. With this indication of the size of the skeleton of the tongue, is combined a more certain proof of the extent of its soft, and especially its muscular parts, in the magnitude of the foramen, for the passage of the lingual or motor nerve (c. fig. 2 and 3). This foramen, (the anteriot· condyloid,) in the present specimen, is the largest of those which perforate the walls of the cranium, with the exception of the foramen magnum; it is fully twice the size of that which gives passage to the second division of the fifth nerve; its area is oval, and eight lines in the loug diameter, so that it readily admits the passage of the little finger. It is only in the Ant-eaters and Pangolins that we find an approximation to these proportions of the foramen for the passage of the muscular nerve of the tongue; and the existing Myrmccophagous species even fall short of the larger fossil in this respect. Some idea of the size of the lingual nerve, and of the organ it was destined to put in motion, may be formed, when it is stated that the foramen giving passage to the corresponding nerve in the Giraffe,-the largest of the Ruminants, and having the longest and most muscular tongue in that order,- i8 scarcely more than one-fonrth the size. With these indications of the extraordinary development of the tongue, we are naturally led, in order to cany out a closer and more detailed comparison of the fossil in question, to that group of mammalia in which the tongue plays the chief part in the acquisition of the food. 'l'he size, form, and position of the occipital condylc,-the magnitude of the occipital foramen, (which must here have somewhat exceeded three inches in the transverse diameter,) - the slope of the occipital surface of the cranium from below, upwards and forwards, at an angle of 60° FO IL MAMMALIA . 59 with the base of the cranial cavity-each and all attest the close affinities of the present animal to the Edcntata. More decisive evidence of the same relation hip will be adduced ft·om the organization of other parts of the cranium. The glenoid articular surface (a, fig. 2, PJ. XVI.) is an almost flattened plane, wider in the transverse than in the longitudinal direction ; and, as in the genera Myrmecopltaga and Manis, it is not defended behind by any descending process. In its general form it resembles the glenoid cavity of Orycteropus more than that of the preceding Edentates; but, in Orycteropus, the articulation is defended posteriorly by a descending process of the zygoma, and it is also situated relatively closer to the os tympanicum. Had the Glossotlte1·ium teeth? The extent of the temporal muscle, which i indicated by the rugged surface of the temporal fossa, and by the well-marked boundary, formed by a slightly elevated bony ridge, which extends to near the line of the sagittal 8uture, together with the size of the zygomatic portion of th temporal bone, and the remains of the oblique suture by which it was articulated to the malar bone, enables me to answer this question confidently in the affirmative. They will probably be found to be molar teeth of a simple structure, as in the Orycteropus. The evidence just alluded to of the existence of an os malre is interesting, because this bone is wanting in the Pangolins; and its rudimental representative in the true Ant-eaters does not reach the zygomatic process of the tempoml bone, which consequently has no articular or sutural surface at its anterior extremity. In the presence, therefore, of the surface for the junction of the os mahe, and th consequent evidence of the completion of the zygomatic arch, we learn that the Glossothere was more nearly allied to the Armadillos and Orycterope. That its affinity to the latter genus was closer than to the At·madillos we have mo t intere. ting evidence in the form and loose condition of the tympanic bone: it is represented of the natural size at fig. 4, J>J. XVI. Through the care and attention devoted to his specimens by their gifted discoverer, this bone was preserved in situ, as represented at d, fig. 1 ; but it had no o. seous connection with the petrous or other elements of the temporal bone, and could be displacerl and replaced with the same ease as in the Orycterope. This bony frame of the membrana tympani, in the Glossothere, describes rather more than a semicircle, having the horns directed upwards; it ha8 a groove, one line in breadth, along its concave margin, for tho attachment of the ear-drum, and sends down a rugged process, half an inch long, from its lowet· margin. In the Dasypodes and Mynnecoplwgce, th tympanic bone soon becomes anchylosecl with the other parts of the temporal; it is only in Orycteropus, among the existing insectivorous Bmta or Edentata, that it manifests throughout life the freta] condition of a distinct bony hoop, deficient at the uppe1· part. The os tympanicum of Orycteropus, however, differs from that of |