110 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. \Vol.YI. 



amine them iu the closed wing, extend beyond the head of the humerus. 

 In this position also the radius occupies a higher level than the ulna, 

 and is the innermost bone of the two. The radius is slender, the trans- 

 verse diameters of its subcylindrical shaft varying but little throughout 

 its extent, though its extremities are expanded. From the elbow-joint, 

 when the two bones are in position, it at first diverges from the ulna at 

 a moderate curve, to approach that bone again to nearly absolute con- 

 tact at the junction of middle and distal thirds, by a more gentle curve ; 

 from this latter x)oint it lies i)arallel with the ulna to the wrist. The 

 head of the radius is elliptical, being crowned by a depression for artic- 

 ulation with the oblique facet on the distal end of the humerus. Beyond, 

 below, and to the outer aspect of this facet is another of similar form, 

 though convex for articulation with the ulna, while still more advanced 

 toward the distal end we find the bicipital tuberosity, and, beyond, the 

 minute nutrient foramen ; all of the bones beyond the humerus being 

 non-pneumatic. The distal extremity of the bone in question is termin- 

 ated by a little fan-like expansion that caps the ulna and articulates by 

 its anterior convex margin with the scapho-lunar of the wrist. It is 

 marked above by the longitudinal groove for the tendon of the extensor 

 metacarpi radialis longus. The shaft of the ulna is nearly three times 

 as large as that of the radius. Its outer lialf is straight, its inner curved 

 towards the humerus, thereby increasing, at the proximal moiety, the 

 interosseous space, by the assistance of the opposite curve made by the 

 radius. The stronger end is the one involved in the formation of the 

 €lbow-joint ; here is to be observed the depression for the head of the 

 radius, or the lesser sigmoid cavity, while the articular surface beyond 

 that occupies the entire end of the bone, directed do\^Tiwards, inwards, 

 and backwards, presents for examination the greater sigmoid cavity, the 

 olecranon and coranoid processes, and the cavity for articulation with 

 the oblique facet of the humerus. The greater sigmoid cavity is sub- 

 circular and of some depth ; its lower and produced lip represents the 

 coranoid process, as does its upx)er, better marked, and more tuberous 

 prolongation represent the olecranon of andranatomia. Extending 

 radiad is another concave, quadrate, articular facet for the obhque tuber- 

 cle of the humerus, as the first-mentioned concavity articulates with the 

 ubiar tubercle or trochlea. A little beyond this articular surface are 

 various small tuberosities and depressions for the origin and insertion of 

 muscles. Approaching the wrist, the shaft is seen to be generally smooth, 

 and diminishes in calibre at junction of middle and proximal thirds in 

 the nutrient foramen, while along its entire length, at certain intervals, 

 are the slight elevations for the apices of the quills of the secondaries. 

 The distal extremity of the ulna enters into the formation of the wrist- 

 joint; it is not nearly as large as the proximal end. The articulating 

 surface has a deep mesial cleft in the vertical direction, limited exter- 

 ternally by an elliptical curve, internally by a double, tuberous knob for 

 articulation with the irregularly formed cuneiform of the carpus, while 



