$3tcttaiuirj) of 



$ature. 443 



i and its vesicatory properties are as powerful 

 as the Cantharis of the shops, with which it 

 is said to be mixed in Italy. 



MYLODOX. A gigantic animal, which 

 has long since become extinct, but of whose 

 former existence there can be no doubt ; in- 

 asmuch as a magnificent skeleton of it has 

 been discovered, and is now in the Museum 

 of the Royal College of Surgeons, London. 



The teeth of the Mylodon are eighteen in 

 number, five on each side above and four 

 below : they are simple, long, fangless, of 

 uniform substance and nearly straight, with 

 the exception of the first tooth in the upper 

 jaw, which is slightly curved. From its 

 dentition, therefore, and the peculiar con- 

 formation of the jaws, it is concluded that it 

 fed on the leaves or slender terminal twigs 

 of trees, in this respect resembling the giraffe, 

 the elephant, and the sloth. The extra- 

 ordinary stature of the giraffe raises its 

 mouth with ease to its food ; the trunk of 

 the elephant conveys the food to its mouth ; 

 and the comparatively light weight of the 

 sloth enables him to run along the under 

 side of the boughs till he has reached a com- 

 modious feeding-place : but the Mylodon and 

 his congeners had short and massive necks, 

 and were as bulky as the Rhinoceros ; so 

 that it is apparently impossible they could 

 obtain their food in the same manner as either 

 of the animal* we have mentioned. In his 

 analysis of the osteological structure of the 

 Mylodon, Professor Owen, after alluding to 

 its very perfect clavicles, which have been 

 alternately received as evidence of the bur- 

 rowing and climbing hypothesis, does not 

 admit them to be necessarily essential to 

 those qualities, since the bear and the badger, 

 the one a climbing and the other a burrow- 

 ing animal, are perfectly destitute of them : 

 but from a comparison of the hand of the 

 Mylodon with that of certain ant-eaters, he 

 infers that it was an instrument employed 

 in digging or removing the earth. The great 

 bulk of the posterior extremities, and the 

 corresponding excess of muscular power, as 

 shown by the spinal crest of the sacrum, he 

 regards as farther evidence against the 

 climbing theory ; while he believes that the 

 enormous tail formed a tripod with the hind 

 legs, which could well support the weight of 

 the animal, and leave the anterior limbs at 

 liberty. " If the foregoing physiological in- 

 terpretation of the osseous frame- work of the 

 gigantic extinct sloths be the true one," 

 says Mr. Owen, " they may be supposed to 

 have commenced the process of prostrating 

 the chosen tree by scratching away the soil 

 from the roots ; for which office we find in 

 the Mylodon the modern scansorial fore-feet 

 of the sloth modified after the type of that 

 of the partially fossorial ant-eater. The 

 compressed or subcompressed form of the 

 claws, which detracts from their power as 

 burrowing instruments, adds to their fit- 

 ness for penetrating the interspaces of roots, 

 and for exposing and liberating them from 



the attached soil. This operation having 

 y effected by the alternate action of 

 the fore foot, aided probably by the ungiii- 



been dul 

 the fore 

 oiilatfc digits of the hind feet, the long and 



curved fore-claws, which are habitually 

 flexed and fettered in the movements of ex- 

 tension, would next be applied to the op- 

 posite sides of the loosened trunk of the tree: 

 and now the Mylodon would derive the full 

 advantage of those modifications of its fore- 

 feet by which it resembles the Bradypus ; 

 the correspondence in the structure of the 

 prehensile instruments of the existing and 

 extinct sloths, extending as far as was com- 

 patible with the different degrees of resist- 

 ance to be overcome. In the small climbing 

 sloth the claws are long and slender, having 

 only to bear the weight of the animal's light 

 body, which is approximated by the action 

 of the muscles towards the grasped branch, 

 as to a fixed point. The stouter proportions 

 of the prehensile hooks of the Mylodon 

 accord with the harder task of overcoming 

 the resistance of the part seized and bringing 

 it down to the body. For the long and 

 slender branchial and anti-branchial bones 

 of the climbing sloth we find substituted in 

 its gigantic predecessor a humerus, radius, 

 and ulna of more robust proportions, of such 

 proportions, indeed, in the Jlylodon robust us 

 as are unequalled in any other known ex- 

 isting or extinct animal. The tree being 

 thu.s partly undermined and firmlj grappled 

 with, the muscles of the trunk, the pelvis, 

 and hind limbs, animated by the nervous 

 influence of the unusually large spinal 

 chord, would combine their forces with those 

 of the anterior members in the efforts at 

 prostration. And now let us picture to our- 

 selves the massive frame of the Megatherium, 

 convulsed with the mighty wrestling, every 

 vibrating fibre reacting upon its bony attach- 

 ment with a force which the sharp and 

 strong crests and apophyses loudly bespeak : 

 extraordinary must have been the strength 

 and proportions of that tree, which, rocked 

 to and fro, to right and left, in such an em- 

 brace, could long withstand the efforts of its 

 ponderous assailant." 



MYOCHAMA. A genus of Mollusca, of 

 which only one species is known (the H. 

 cmomioides of New South Wales), described 

 by Mr. Sowerby as " inequivalve, irregu- 

 lar, attached, sub-equilateral ; attached valve 

 flat, with two marginal, diverging teeth, and 

 one end of a little testaceous appendage fixed 

 between them by a horny cartilage ; frte 

 valve convex, with umbo incurved, and two 

 very minute diverging teeth, between which 

 the other end of the testaceous appendage 

 is placed ; external surface of both valves 

 conforming to the grooves or undulations of 

 the shell to which the specimen is attached ; 

 muscular impressions two in each valve ; 

 palleal impression with a short sinus." 



MYOXTJS. [See DORMOUSE.] 



MYRAPETRA. A genus of Hymenop- 

 tera, which constructs a singular nest. [See 

 WASP.] 



MYRIAPODA. The name given to the 

 lowest class of articulated animals ; in- 

 cluded by some naturalists among the in- 

 sects, and bearing considerable affinity to 

 them ; but differing from that large class in 

 the absence of wings, and in the body being 



