8 PROFESSOR OWEN ON THE OSTEOLOGY OF 



noted in anthropotomical descriptions of the bone) ; secondly, its more slender and 

 less bent shaft ; thirdly, the better definition and greater depth of the grooves for the 

 three tendons acting on the thumb, at the back part of the distal expansion ; fourthly, 

 the more produced styloid process (/) ; whilst the tuberosity above it for the attach- 

 ment of the supinator longus is much less developed than in either the Gorilla or Chim- 

 panzee. 



UZna.— Plate V. 



The ulna of the Gorilla (figs. 1-3), like the radius, is less straight than in Man 

 (fig. 8), contributing thereby to augment the breadth of the strong bony frame of the 

 fore-arm. It is shorter than the humerus, but in a less degree than in Man. The upper 

 half of the shaft is trihedral, the posterior surface being convex, the inner one flat, the 

 outer one slightly concave; this half gradually expands, as it rises, to form the wide and 

 deep surface (fig. 3, 6, c), concave lengthwise, convex transversely, called ' great sig- 

 moid cavity ' in anthropotomy, for the interlocking articulation with the ulnar trochlea 

 of the humerus ; the back wall of the cavity developes a powerful tuberosity projecting 

 ' ulnad ' or inwards as well as backwards : the upper part of the olecranon (e) is a broad 

 subtruncate bent plate of bone, smooth behind, and with its radial border gliding 

 upon the articular surface extended from the humeral trochlea upon the corresponding 

 boundary of the great anconeal depression. The olecranon is thicker and broader in 

 proportion to its length than in Man. The coronoid process developes a large tubercle 

 below its inner or ulnar border for the origin of the flexor sublimis digitorum. The 

 articular surface, called ' lesser sigmoid cavity ' {d), for the rotatory joint with the radius, 

 has relatively more transverse extent than in Man. The fossa below the coronoid 

 process and the tuberosity beneath the fossa, for the insertion of the ' brachialis 

 anticus,' are very strongly marked. 



The great sigmoid cavity is unequally divided into the facets b and c, fig. 3, by the 

 longitudinal prominence, as in Man (fig. 12) ; but the marginal notches are less 

 marked ; there is a shallow depression for the synovial organ called ' Haversian gland,' 

 whence a linear groove extends to the lesser sigmoid cavity {d, fig. 1). The shaft of the 

 ulna, in a front view, as in fig. 3, presents two slight opposite curves, the upper one 

 concave, the lower one convex, on the ulnar or inner aspect. Viewed sideways, as in 

 fig. 1, the whole bone has a slight bend convex backwards. The lower half of the shaft 

 becomes subcylindrical as it descends. The ridge, commencing below the lesser sig- 

 moid cavity, is strongly marked and more vertical than in Man ; the surface for the 

 attachment of the anconeus muscle between this and the ridge descending from the 

 outer side of the olecranon is well defined. The distal end of the ulna suddenly ex- 

 pands into a convex reniform articular surface, thickest at the middle, where it plays 

 upon the lateral concavity of the radius. The styloid process (g) is less produced in 

 the skeleton of the old male Gorilla (PI. XIII.) than in the outline restoration in the 



