MR. 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 (Pl. 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 Tyoglodytes. 
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 (P]. XXXVIII. fig. 1) surface for the flexor profundus 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 (Pl. XX XVIII. fig. 14). As in the higher forms, its direction is proximad. 
The internal surface of the shaft is smooth, but more convex than in Man 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 (Pl. XX XVIII. 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 pollex and index) is generally as flat as in Man, and more 
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 the flewor 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 Chimpanzee, 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 (Pl. XXXVIIL fig. 1a). Very rarely, however, the radial margin is enormously 
produced’, In the Orang, unlike the higher forms, the upper part of this margin does 
1 As in the specimen in the Collection of the British Museum, which bears the No. 32, from the MS. catalogue 
of the Zoological Society’s Collection. 
VOL. VI.—PART IY. 2D 
