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Show 7H ZOOLOGY OF THE YOYAGE OF THE BEAGLE. the known difference in the position of the occipital plane, which in the Glosso-there corresponds w.t th t 11 at I·l l t 11 e ll':;Lr! J1 ·m ec o'J "J'1't ao"='· a ·•w d Bmdypu-s ' we shal. l be justified in continuing to regard them, until evidence to the contrary be obtamed, as belono-ing to distinct genera. . The parietal bones present an oblong regular quadrate figure, the sagt.ttal nture runm·n g parallel w1· t b t1 w squamous, an d tl1e f'rontal with. the lambdmdal uture; there is scarcely any trace of denticulations in the sag~ttal s~turc; ~he bones are of remarkable tbickue s, varying, at this suture, from SIX to mne 1ine , and their opposed surfaces are locked together by narrow ridges, which lightly radiate from the lower to the upper part of the uniti.ng .~m·face: the ubstance of the bone consists of an uniform and pretty dense dtploe; and there are no sinuses developed in it. We can hardly regard the extraordinary air-cells which occupy the interspace of the two tables of the skull in the parietal and o cipital bones of the Glossothere (Pl. XVI.. fig. 3) as a difference depending merely on age. The frontal and rethmoid hones are broken away in the presentcmnium. Th 'phenoid commence two inches in front of the foramen occipitale; the fractured tate of the skull does not allow its anterior or lateral limits to be accurately defin d; it body is occupied with large air-sinuses; the only part, indeed, of this bone which is exposed to observation is that which forms part of the floor of the cranium ; and this we shall now proceed to describe, in connexion with the other peculiarities of the cranial cavity, (fig. 1. Pl. XXIII.) The body of the sphenoid i impre · erl on its cranial surface with a broad and shallow sella turcica(a), bounded by two grooves, (b b,) leading forwards and inwards from the carotiu toramina (c) ; the line of suture between the sphenoid and occipital bones runs along a lio·ht transverse elevation (d), which bounds the sella posteriorly; this suture i partially obliterated: a slight median protuberance (e) bormds the sella turcica anteriorly; there are ncithct· anterior nor posterior clinoid processes. External to the carotid channel there is a wide groove (f ) leading to the foramen oval (g ) ; this foramen is about one-third smaller than in the Glossothere, anrl therefore, as compared with the anterior condyloid foramina, indicates that the tongue wa endowed with a gTeat r proportion of seu itive than motive power in the Scelidothcre: but in rea oning on the ize of this nerve, it must be remembered that in botlt animal certain branches, both of the second and third divisions of the fifth pair of nerves, arc 1o be as~ociated with the per istence of large dental pulp , of whtch they regulate the secreting power. Anterior to the foramen ovale, and at the termination of the sam8large common groov , lodging the trunk of the fifth ~air of nerves Is the fora1uen rotund urn (It); this leads to a very long canal, the dwmeter of which is five lines, being somewhat less than that for the third divi ion of the fifth pait·. The anterior sphenoid i broken away, so that no ob ervation can be made on the optic foramina. FOSSIL MAMMALIA. 79 The basilar process of the occipital bone is perforated at its middle by two small foramina(i) on the same transverse line, about half an inch apart. In the Armadillo these foramina do not exist: in the Orycterope they are present, but open ueneath an overhanging ridge, which is continued from them to the upper part of the anterior condyloid foramen on each side. The sella turcica of the Orycterope is deeper and narrower than in the Scelidothere; and is separated from the basilar occipital process by a transverse ridge, which sends forwaru two short clinoid processes; two smaller anterior clinoid processes project back wards from the angle of the anterior boundary of the sella turcica. The foramina ovalia and rotuuda open in the same continuous groove, as in the Glossotbere and Scelidothere, but they are relatively wider apart; and the canal for the third division of the fifth pair is shorter, and runs more directly outwanls. The petrous Lone iu the Scelidothere is relatively larger than in the Glossothere, but this probably arises from the precocious development of the organ of hearing in the present immature specimeu in obedience to the general law. The trunk of the fifth pair of nerves does not impress it with so deep and well defined a groov as in the Glossothere; the elliptic internal auditory foramen(/.:) is situated about the miudle of the posterior surface; behind this is the aqueduetus vestiuuli; and immediately posterior to the petrous bone is the foramen jugulare (l): the shape of the os petrosum agrees more with that of the Armadillo than with that of the Orycterope. An accidental fracture of the right os petrosnm demonstrates its usual dense and brittle texture, and at the same time has exposed the coclllea with part of its delicate and beautiful lamina spiralis. The conservation of parts of the organs of vision in certain fossils, has given rise to arguments which prove that the laws of light were the same at remote epochs of the earth's history as now; and the structures I have just mentioned, in like manner, demonstrate that the Jaws of acoustics have not changed, and that the extinct giants of a former race of quadmpeds were endowed with the same exquisite mechanism for appreciatin•r the vibrations of sound as tlwir existing congeners enjoy at the present day. The brain, being regulated in its development by laws analogous to those which govern the early perfectiou of the organ of hearing, appears to have been relatively larger in the Scelidothere than in the Glossothere: it was certainly relatively longer; the fractured cranium gives us six inches of the antero-posterior diameter of the brain, but the analogy of the Orycterope would lead to the inference that it extended further into the part which is broken away. The greatest transverse diameter of the cranial cavity is four inches eight lines: these dimensions, however, are sufficient to show that the brain was of very small relative size in the Scelidothcre; and, both in this respect, and in the relative position of its principal masses, the brain of the extinct Eden tal closelyaccords with the general character of this organ in the existing species of the same Order. We perceive by the obtuse |