t40 Royal Society. 



inferior angle bent outwards, increasing the depth of the subspinal 

 fossa : there is a rudiment of a second spine, below the normal one : 

 the acromion is expanded, produced and confluent with the coracoid ; 

 and the supraspinal fossa is perforated by a circular aperture. The 

 clavicle has a well-marked sigmoid flexure, equally-developed obtuse 

 extremities, without any articular surface. The humerus is remark- 

 able for the enormous development of ridges for the attachment of 

 the muscles, especially at its distal end : the inner condyle is not 

 perforated as in the Megalonyx\ it is devoid of a medullary cavity. 



The ulna and radius are next described. The carpus consists of 

 seven bones, three of which are proper to the first row, three to the 

 second, and one is common to both : the latter answers to the *sca- 

 phoides' and * trapezium' in the human wrist, and articulates with the 

 radius above, and the rudiment of the metacarpal of the pollex below. 



Only four digits are developed, the first or ' pollex ' being obso- 

 lete. The ' index * or second digit has three phalanges, the last sup- 

 porting a large claw, and being twice as long as the two preceding 

 phalanges. The proximal and middle phalanges of the * digitus 

 raedius' are confluent. The ungual phalanx is shorter than that of 

 the index, but has twice its vertical breadth. The metacarpals 

 progressively increase in length from the first to the fifth. The 

 fourth digit or 'annularis' has three phalanges, the last being un- 

 guiculate and longer than that of the 'medius.' The fifth digit 

 has only two very short rounded phalanges, which were doubtless 

 buried in a thick callous outer border of the foot, on which the 

 Megatherium rested when applying the foot to the ground. 



The pelvis shows the conversion of the ischiadic notch into a 

 foramen by the anchylosis of the ischia with the posterior sacral 

 vertebrae, and the union of the ossa pubis at a short anteriorly pro-' 

 duced symphysis. The ilia are extraordinary for their vast breadth, 

 and the thickness of the rugged labrum ; indicative of the enormous 

 muscular forces, of which this conspicuous part of the skeleton was 

 the centre. 



The femur is hardly less remarkable for its breadth and strength. 

 The head is devoid of an impression for the ligamentum teres: but 

 from the dimensions of the hemispheroid cavity receiving it, the 

 author calculates that the muscles are aided in retaining the head 

 of the femur in its place by an atmospheric pressure, with the baro- 

 meter at 30 in., of not less than 660 pounds. At the distal end of 

 the femur there is a great angular projection above the outer con- 

 dyle. The rotular surface is continuous with that upon the outer 

 condyle, but not with the inner one. The tibia and fibula are anchy- 

 losed together at both their extremities. Besides the patella in front 

 of the knee-joint, there is a sesamoid ' poplitella' behind, wedged 

 between the outer condyle and the tibia; which was doubtless im- 

 bedded at its base in the femoro-tibial articular capsule, and gave 

 insertion to the tendon of the popliteus muscle. This sesamoid is 

 not to be confounded with the ' fabella,' developed in many quadru- 

 peds in the origin of the gastrocnemius, behind one or both condyles 

 of the femur. The most peculiar feature in the tibia of the Mega- 

 therium is the form of the distal articular surface: especially the 



