94 THE BONES OF THE UPPER LIMB. 



and internal condyles (the epicondyle and epitrochlea of Chaussier). The internal 

 condyle is the more prominent, and is slightly inclined backwards, forming 

 posteriorly a shallow groove in which the ulnar nerve lies : its extremity is marked 

 anteriorly by an impression to which the common tendon of the superficial 

 pronato-flexor muscles of the forearm is attached. On the external condyle are seen, 



1, a mark for the common tendon of some of the muscles of the back of the forearm ; 



2, below and internal to this, a smaller impression for the anconeus ; and 3, between 

 the foregoing and the margin of the radial articular surface, a pit in which the 

 external lateral ligament of the elbow-joint is attached. The inferior articular 

 surface is divided into two parts. The external part, articulating with the radius, 

 consists of a rounded eminence directed forwards, called the capitellum, and a 

 groove internal to it ; it does not extend to the posterior surface. The internal part, 

 the trochlea, articulates with the ulna, and extends completely round from the 

 anterior to the posterior surface of the bone; it is grooved in the middle like the 

 surface of a pulley, and is somewhat broader behind than in front ; anteriorly, its 

 margins are inclined downwards and inwards ; posteriorly, upwards and outwards, so 

 that, seen from behind, it occupies the middle part of the bone. In front, the internal 

 margin of the trochlea is the more prominent, and forms a convexity parallel to the 

 groove ; behind, the external margin is slightly more prominent. Above the 

 trochlea posteriorly is a large and deep pit, the olecranon fossa, which receives the 

 olecranon process of the ulna in extension of the forearm ; and above it anteriorly, 

 separated from the olecranon fossa only by a thin lamina of bone, is the much smaller 

 coronoid fossa, which receives the coronoid process in flexion. Above the capitellum 

 is a shallow depression the radial fossa, into which the head of the radius is 

 pressed in complete flexion. 



The humerus, in its natural position with the arm hanging by the side, has a 

 slight inclination from above downwards and inwards, and is also in a condition of 

 what may be termed strong internal rotation, i.e., the so-called anterior surface looks 

 very much inwards, and the internal condyle is directed more backwards than 

 inwards. The bone is almost completely covered by muscles ; the upper extremity 

 is thickly covered by the deltoid, which it pushes up, and thus gives roundness to 

 the shoulder : the shaft is entirely surrounded : both condyles are subcutaneous, the 

 internal being prominent, while the appearance of the external varies as the forearm 

 is moved. When the elbow is bent the capitellum projects under its muscular 

 covering, and forms the rounded prominence outside the point of the elbow. 



The average length of the humerus in the adult male is about 13 inches, in the female 12 

 inches. It is nearly one-fifth of the stature of the individual, and somewhat more than twice 

 as long as the clavicle. 1 



The major axes of the upper and lower extremities of the humerus do not lie in the same 

 plane, but cross one another at an angle, known as the angle of torsion, which varies greatly 

 in different individuals, but averages about 20 in Europeans, and 35 in Negroes. The axis 

 of the upper end forms a smaller angle anteriorly with the sagittal plane than that of the 

 lower end. In quadrupeds the torsion is usually about 90. (Broca, Rev. d'Anthrop., 1881.) 



Varieties. A small hook-like process, with its point directed downwards, is not un- 

 frequently found in front of the internal condylar ridge, the supracondylar process. From its 



1 On the length and proportions of the long bones in different races of men may be consulted 

 Humphry, "A treatise on the human skeleton"; Topinard, " Elements d'anthropologie geVerale "; 

 Turner, " Challenger " Reports, Zoology, xvi ; Rollet, ' ; Mensuration des os longs des membres," 1889. 



It may here be remarked also that the limb-bones of the two sides are seldom of equal length. In most 

 cases the bones of the tipper limb (humerus + radius) are longer on the right side, the difference being 

 commonly about one-third of an inch, and rising occasionally to three-quarters of an inch. The 

 increased development is probably associated with the greater use of the right hand. In the lower limbs 

 the differences are not so marked, and the excess appears to be more frequently on the left side. These 

 differences do not exist at birth. (Garson, Journ, Anat., xiii, 502 ; Rollet, op. cit. ; Gaupp, " Maass- 

 und Gewichts- Differenzen zwischen den Knochen der rechten uud linken Extremitaten," Diss., 

 Breslau, 1889.) 



