ME. ST. G. MIVART ON THE SKELETON OF THE PRIMATES. 185 



the shaft may be seen to have a sigmoid curvature, which is convex ulnad below, above 

 concave. This curvature is more marked than is generally the case in Man, or than 

 sometimes in the Gorilla ; it is less so, however, than in the Chimpanzee. When the 

 bone is viewed laterally (PI. XXXVIII. figs. 2 & 4), the shaft is seen to present a 

 curve, convex backwards, which is slightly more marked than in Man, but not quite so 

 much so as in Troglodytes. 



The body, or shaft, of the ulna is more rounded than in Man or Troglodytes, and can 

 hardly be said to present the three surfaces and margins usually described as existing in 

 the human ulna, the parts which correspond to the anterior and posterior margins of 

 Man being so ill defined. The ulna tapers distally, but, on account of the length of 

 the bone, more gradually than in the higher forms. 



The anterior surface of the shaft has a more or less flattened, and even sometimes deci- 

 dedly concave (PI. XXXVIII. fig. 1) surface for ih.e flexor profundtis digitorum; and 

 the nutrient foramen, much more conspicuous than in Man or Troglodytes, is more or 

 less remote from the radial margin of the bone, and rather below the uppermost third of 

 its total length (PI. XXXVIII. fig. 1 h). As in the higher forms, its direction is proximad. 

 The internal surface of the shaft is smooth, but more convex than iuMan and Troglodytes, 

 except at its summit, where the concavity is more extensive than in them, reaching as it 

 does somewhat more nearly to the superior limit of the olecranon (PI. XXXVIII. fig. 2). 

 The posterior, or radial, surface of the shaft is less strongly divided into two parts 

 than in Man and the Gorilla, though the lower and much larger one (serving to give 

 origin to the extensors of the poUex and index) is generally as flat as in Man, and moie 

 so than in Troglodytes ; very rarely it is strongly concave. 



An anterior margin can sometimes hardly be distinguished, and never extends, as in 

 Man, from the coronoid process to the lower extremity of the ulna. Sometimes, how- 

 ever, it can be traced from that process down to somewhat below the level of the 

 medullary foramen. Similarly the posterior margin of the human ulna (which extends 

 from the olecranon to the styloid process, and gives attachment to an aponeurosis com- 

 mon to t\ie flexor profundus digitorum, the flexor carpi ulnaris, and the extensor carpi 

 ulnaris) is in the Orang represented by a prominence which ceases to be distinguishable 

 at about the middle of the ulna. 



The external or radial margin begins above at the posterior margin of the lesser 

 sigmoid cavity, and extends rather more than two-thirds down the bone. It is not so 

 sharp as in man and the Chimimnzee, but it is more so than in the Gorilla. The sharp- 

 ness, however, generally only extends along about the middle third of the bone, which 

 at that part is considerably roughened for a greater or less extent close to the radial 

 border (PI. XXXVIII. fig. 1 a). Very rarely, however, the radial margin is enormously 

 produced'. In the Orang, unlike the higher forms, the upper part of this margin does 



' As in the specimen in the Collection of the British Museum, which bears the No. 32, from the MS. eatalognc 

 of the Zoological Society's Collection. 



VOL. VI. PART IV. 2 D 



