442 ANATOMY OF VERTEBRATES. 



in some Rodents, sends down a process : the coracoid is a mere 

 tuberosity : the glenoid cavity is shallow, twice as long as broad : 

 it looks downward, the scapula rising vertically above the hu- 

 merus. 



The humerus, ib. 53, has the great tuberosity extended antero- 

 posteriorly, and rising above the sessile hemispheric head of the 

 bone : the deltoid ridge descends below the middle of the bone : 

 the occipital groove is deep : the ectocondylar ridge rises straight 

 for one-third the length of the humerus, and forms a low angle 

 before subsiding upon the shaft. The distal articular surface is 

 a simple shallow trochlea. The proximal ej^physis is in two 

 parts, one capping the head, the other the great tuberosity : the 

 distal epiphysis is single. The centre of the shaft is almost 

 Avholly occupied by a delicate cancello-reticulate structure. 



The antibrachial bones are distinct and cross obliquely, the ra- 

 dius passing in front of the ulna to the inner side of the carpus, 

 as in the Megathere : but the prone position of the fore foot 

 cannot here be changed ; for the head of the radius, ^g. 297, 55, 

 is wedged between two processes of the ulna, ib. 54, and the ex- 

 panded distal half has a rough ligamentary union mth that bone. 

 The proximal articulation with the humerus is transversely elon- 

 gate, partly convex and partly concave. The ulna is the larger 

 bone ; its olecranon is thick and convex : the proximal epiphysis 

 covers only this process : the distal one forms the articulation 

 for both radius and carpus. This segment includes a small sca- 

 phoid, fig. 297, 5, a larger lunare, /, cuneiforme, c, and pisiforme, 

 with the usual four bones of the distal row. In the scaphoid, 

 the small surface for the radius is remote from that which joins 

 the trapezium, t, and trapezoides, d. The single surface of the 

 pisiforme has two facets, the smaller of which joins the ulna. 

 The trapezium extends along half the metacarpal of the index. 

 The phalanges, tw^o in the first and three in each of the other 

 four digits, are broad and short, especially the last, which is 

 firmly encased in the corresponding division of the hoof. 



The hind limbs and pelvic arch present opposite proportions to 

 those in the Megatherioids : the skeleton of the extinct Probos- 

 cidian leaf-eater, fig. 297, contrasts singularly in this respect 

 with that of the extinct Megatherioid one, fig. 267. To both 

 these giants among land quadrupeds the forests of the primeval 

 world afforded sustenance ; but their ways of obtaining it were 

 difierent, and called for preponderance of developement in the 

 hind part of the skeleton in the one, and of the fore part in the 

 other. The pelvis descends vertically at almost a right angle 



