46 



length : in their bony structure they include a complete clavicle with the scapula, a 

 humerus, an antibrachium consisting of fully developed and reciprocally rotating 

 radius and ulna, the carpus, metacarpus and four digits ; and manifest, in short, all 

 the main perfections of brachial structure, save the opposable thumb, observable in 

 the Mammalian class. These perfections, moreover, are associated with proportions 

 and processes indicative of enormous strength, and bespeak a limb fitted not only to 

 take its full share in the support of the body, but to be employed in operations in 

 which unusual resistance has manifestly to be overcome. In no respect, perhaps, 

 does the Megatherium more strikingly differ in its osseous structure from the existing 

 quadrupeds of corresponding bulk, than in the bony fulcra of the anterior extremity. 



The scapula (Plate I. n, and Plate XVIII. figs. 1 & 2) presents a vast expanse of 

 bone, with a double spinous process ; the normal one expanding into a large acromion 

 which is continued into and is confluent with the coracoid process. The scapula 

 presents an inequilateral triangular form, of which the acromion is the apex ; the 

 main body or plate of the bone approaches to the form of the geometrical trapezium, 

 except that the extent of the posterior border or base is such as to destroy the 

 parallelism of the upper and lower borders. The upper border (b, c) is the shortest ; 

 but, in one specimen, owing to the greater development of the basal border it appears 

 to begin, as in Plate I., at the part of the base marked a in Plate XVIII., and to 

 form a low angle, as if continued about one-fourth of the distance from the base 

 parallel with the lower border, whilst the rest of the costa inclines downwards or 

 converges towards the neck of the scapula, with a slight concave outline. The upper 

 border increases in thickness as it passes into the origin of the coracoid, c. The 

 base of the scapula, from the point a, is straight as far as the origin of the spine ; 

 it then bends, with a convex curve, and increases in thickness to the inferior angle of 

 the scapula (d) close to which commences the second or lower spine. The inferior 

 costa of the scapula (d) extends forwards straight and parallel with the lower spine, 

 for some way, and is so continued into that spine that the fore-part of this might be 

 regarded as the inferior and anterior angle of the scapula bent outwards; but it 

 curves down to what may be more correctly considered as that angle at e, fig. 1, 

 Plate XVIII. 



The normal spine of the scapula, notwithstanding its being the superior of the two, 

 commences at only one-fourth of the entire base of the bone from the inferior angle ; 

 it is thence continued forwards, gradually rising or gaining depth, parallel with the 

 inferior costa, and thus marks out a very large proportional extent of the outer 

 surface of the bone for the supra-spinal fossa, Plate I. si. As the spine advances it 

 increases in breadth as well as depth, until it springs clear of the main body of the 

 bone as the acromial process, k. This large, thick and rough process arches forward 

 and upward over the glenoid articular cavity (g), and meets and coalesces with the 

 coracoid (c), spanning the anterior outlet (/) of the supra-spinal fossa by a strong 

 and broad bridge of bone. Through the reciprocal modification of the coracoid, the 

 passage for certain vessels and nerves, which is usually in Mammals a mere notch of 

 the upper border of the scapula, is converted into a complete foramen, ft. 



