715 



MEGATHERIID^E. 



MEQATHERIID-'E. 



748 



Glossotherium, (Owen). The genus is founded on a fragment of a 

 cranium in Mr. Darwin's collection, discovered in the bed of the same 

 river in Banda Oriental with the skull of the Toxodon. The fragment 

 includes the parieties of the left side of the cerebral cavity, the 

 corresponding nervous and vascular foramina, the left occipital condyle, 

 a portion of the left zygomatic process, and, though last, not least, 

 the left articular surface of the lower jaw. No tooth, no locomotive 

 extremity, was present to lend its aid; and yet, upon the slender 

 materials above stated, Professor Owen has been enabled to give generic 

 distinction to the animal to which they belonged, and to fix its place 

 in the animal series satisfactorily. 



Professor Owen remarks, that the importance of the articular 

 surface of the lower jaw in the determination of the affinities of a 

 fossil animal has been duly appreciated since the relations of the 

 motions of the lower jaw to the kind of life appointed for each animal 

 were pointed out by Cuvier; but he observes that we should be 

 deceived if we were to establish, in conformity with the generalisation 

 laid down by Cuvier, our conclusion, from this surface, of the nature 

 of tlie food of the extinct species under consideration; for the shape 

 of the glenoid cavity is such as to allow the lower jaw free motion in 

 a horizontal plane from right to left, and forwards or backwards, like 

 the movements of a millstone : " Nevertheless," continues Professor 

 Owen, " I venture to affirm it to be most probable that the food of 

 Gloatotitfrium was derived from the animal and not from the vegetable 

 kingdom, and to predict, that when the bones of the extremities shall 

 be discovered, they will prove the Glossothere to be not an ungulate 

 but an unguiculate quadruped, with a fore foot endowed with the 

 movements of pronation and supination, and armed with claws, 

 adapted to make a breach in the strong walls of the habitations of 

 those insect societies upon which there is good evidence, in other 

 parts of the present cranial fragment, that the animal, though as large 

 as an ox, was adapted to prey." 



The data on which Professor Owen rests this affirmation, are, in 

 the first place, a remarkable cavity situated immediately behind the 

 tympanic bone, of nearly a regular hemispherical form and an inch in 

 diameter. The surface of this cavity does not appear to have been 

 covered with articular cartilage, because it is irregularly pitted with 

 many deep depressions, and Professor Owen concludes therefore that 

 it served to afford a ligamentous attachment to the styloid element of 

 a large oa hyoides. In addition to this evidence of the size of the 

 bones of the tongue, there is a more certain indication 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, which anterior 

 condyloid foramen is larger than any of those which perforate the 

 cranium, with the exception of the great foramen ; it is eight lines in 

 the long diameter, and readily admits the passage of the little finger. 



The Professor remarks that it is only in the Ant-Eaters and 

 Pangolins that we find an approximation to these proportions ; and 

 that in the Giraffe, the largest of ruminants, and having the longest 

 and most muscular tongue in that order, the foramen for the corres- 

 ponding nerve is scarcely more than one-fourth the size of that of 

 Glouot/ierium. In the other parts of the cranium Professor Owen finds 

 more decisive evidence of the relationship of this extinct edentate to 

 the genera M yrmecophoga and Manii. 



The question, Had the Oloitotherium teeth ? is answered by the 

 Professor in the affirmative, from the rugged surface of the temporal 

 fossa indicating an extensive temporal muscle ; from the well-defined 

 boundary, formed by a slightly-elevated bony ridge, extending to 

 near the sagittal suture ; the size of the zygomatic portion of the 

 temporal bone, and the remains of the oblique suture by which it 

 was articulated to the malar bone ; and he is of opinion that they will 

 probably be found to be molar teeth of a simple structure, as in the 

 Orycteroput. 



Here is evidence of the existence of an os mala;. This bone is 

 wanting in the Pangolins ; in the true Ant-Eaters it does not reach 

 the zygomatic process of the temporal bone. From this evidence of 

 the completion of the zygomatic arch, the Professor concludes that 

 /ilottotlicrium was more nearly allied to the Armadilloes and Oryclero- 

 put; and from the form and loose condition of the tympanic bone, 

 which, through the care and attention of Mr. Darwin, was preserved 

 in situ, that the affinity of the animal was closer to Orycteropus than 

 to the Armadilloes : but the tympanic bone of Orycteroput differs from 

 that of Glouol/ierium in forming part of the circumference of an 

 ellipse whose long axis is vertical, and in sending outwards from its 

 anterior part a convex eminence, which terminates in a point directed 

 downwards and forwards : in the distance from the origin of the 

 zygoma to the occipital plane, which is relatively greater in Gloaso- 

 therium than in Orycteropus, the former is more similar to Myrmeco- 

 I /"I'/'i and Manii. 



The internal surface of the cranial fragment shows that in 

 Glotiotlterium, as in other Bruta, the cerebellum must have been 

 almost entirely exposed behind the cerebrum, that the latter was of 

 mall relative size, not exceeding that of the Ass ; and that it was 

 chiefly remarkable, as in Orycteroput, the Ant-Eater, and Armadillo, 

 for the great development of the olfactory ganglia. 



Such are the leading points on which the establishment of this 

 extinct genus is placed. Our limits do not admit of our following 

 out the interesting details which confirm the view taken by Professor 



Owen, and which c' e reader will find in his ' Fossil Mammalia,' as part 

 of the ' Zoology of the Voyage of Her Majesty's Ship Beagle, under 

 the command of Captain Fitzroy, K.N., edited and superintended by 

 Mr. Darwin, and published with the approval of Her Majesty's 

 Treasury ;' but we think it advisable, with reference to the succeeding 

 fossil species described by the Professor, and here noticed, to give the 

 concluding paragraph in his paper on Qlossotherium. 



"A question," says Professor Owen, "may arise after perusing tlie 

 preceding evidence, upon which the present fossil is referred to a 

 great Edentate species nearly allied to the Orycteropus, whether one 

 or other of the lower jaws, subsequently to be described, and in like 

 manner referrible, from their dentition, either to the Orycteropodoid 

 or Dasypodoid families of Edentata, may not have belonged to the 

 same species as does the present mutilated cranium. I can only 

 answer, that those jaws were discovered by Mr. Darwin in a different 

 and very remote locality ; that no fragments or teeth referrible to 

 them were found associated with the present fossil ; and that, as it 

 would be therefore impossible to determine from the evidence we 

 have now before us which of the two lower jaws should be associated 

 with Glossotherium ; and as both may, with equal if not greater pro- 

 bability, belong to a totally distinct genus, it appears to me to bo 

 preferable, both in regard to ' the advancement of our knowledge of 

 these most interesting Edentata of an ancient world, as well as for 

 the convenience of their description, to assign to them, for the present, 

 distinct generic appellations." 



Mylodon (Owen), a genus of Edentate Megatherioids, founded on 

 some fossil remains described by Dr. Harlan in his ' Medical and 

 Physical Researches," and referred by him to Megalonyx, and on a 

 mutilated lower jaw and teeth discovered by Mr. Darwin among the 

 many interesting novelties which have been the result of that zealous 

 naturalist's researches in the southern division of America. 



The fossil last alluded to was found in a bed of partly consolidated 

 gravel at the base of the cliff called Punta Alta, at Bahia Blanca, in 

 Northern Patagonia, and consists of the lower jaw, with the series of 

 teeth entire on both sides : the extremity of the symphysis, the coro- 

 noid and coudyloid processes, and the angular process of the left ramus , 

 are wanting. 



The teeth are implanted in very deep sockets, and about one-sixth 

 only of the last molar projects above the alveolus ; but the propor- 



Lower jaw of Uylodon, one-sixth natural size. Owen. 



tion of the exposed part increases gradually in the anterior tce*h. 

 This and the relative distance of the teeth will be seen in the following 

 figure : 



External view of right ramus of lower jaw of Mylodon (profile), one-sixth 

 natural size. 



The implanted part of each tooth is simple, of the game size and 

 form as the projecting crown, and with a large conical cavity at the 

 base, for the persistent pulp, and indicating that their growth during 

 life was perpetual. 



Professor Owen remarks that these teeth are composed, as in 

 Bi'adypua, Megatherium, and Meyalonyx, of a central pillar of coarse 

 ivory, immediately invested with a thin layer of fine and dense ivory, 

 and the whole surrounded by a thick coating of cement. 



The exterior surface of the symphysis of the jaw (which is com- 

 pletely anchylosed) is characterised by two oval mammilloid processes, 

 situated on each side of the middle line, and about half-way between 

 the anterior and posterior extremes of the symphysis. Nearly 4 inches 

 behind the anterior extremity of the above process is the large an- 

 terior opening of the dental canal, which is 5 lines in diameter, 

 and situated about one-third of the depth of the ramus of the jaw 

 from the upper margin. The Professor observes that the magnitude 



