joint this accident is very liable to be mistaken for a dislocation of the radius and ulna backwards. The celebrated French surgeon, Dupuytren, used to say "that there was nothing more common than such a mistake." However, the

FIG. 14.

bearing of the condyles with respect to Section to show the trochlea of the olecranon enables us in most cases to

determine the diagnosis. If the olecranon

the humerus.

be higher than the condyles, there is dislocation of the fore-arm; if not higher, it is a case of fracture.

Respecting the condyles, we have to observe, that the internal projects by far the most, since it gives origin to the powerful pronator and flexors of the hand and fingers, namely, to the "pronator radi teres," "flexor carpi radialis," "palmaris longus," "flexor digitorum sublimis," and "flexor carpi ulnaris." The internal lateral ligament of the elbow is also attached to it. The external condyle gives origin, in front, to the common tendon of the extensor muscles; namely, the "extensor carpi radialis brevior," "extensor digitorum communis," and "extensor minimi digiti" and "extensor carpi ulnaris:" behind, it gives origin to the "anconeus." Lastly, the external lateral ligament of the elbow is attached to it.

Centres of ossification.

FIG. 15.

The humerus has seven centres of ossification. There is one for the shaft. About the second year after birth the centre for the head appears; and about the third year, the centre of the tuberosities. About the end of the fifth year, the centres for the head and tuberosities have coalesced, so as to form a large epiphysis on the top of the shaft. It is necessary to remember that this epiphysis includes the tuberosities (as shown in the adjoining wood-cut, fig. 15). On the inner side, the line of junction runs close to the cartilage on the head of the bone: therefore, in the event of separation, the shoulder joint would certainly be implicated. The epiphysis does not unite with the shaft till Epiphysis of the 21st year; so that up to that age it is liable to be separated from the shaft by violence, as we often see in

the head of the humerus.

FIG. 14.

joint this accident is very liable to be mistaken for a dislocation of the radius and ulna backwards. The celebrated French surgeon, Dupuytren, used to say "that there was nothing more common than such a mistake." However, the bearing of the condyles with respect to the olecranon enables us in most cases to determine the diagnosis. If the olecranon be higher than the condyles, there is dislocation of the fore-arm; if not higher, it is a case of fracture.

Section to show the trochlea of the humerus.

Respecting the condyles, we have to observe, that the internal projects by far the most, since it gives origin to the powerful pronator and flexors of the hand and fingers, namely, to the “pronator radi teres," "flexor carpi radialis," "palmaris longus," "flexor digitorum sublimis," and "flexor carpi ulnaris." The internal lateral ligament of the elbow is also attached to it. The external condyle gives origin, in front, to the common tendon of the extensor muscles; namely, the "extensor carpi radialis brevior," "extensor digitorum communis," and "extensor minimi digiti" and "extensor carpi ulnaris:" behind, it gives origin to the "anconeus." Lastly, the external lateral ligament of the elbow is attached to it.

Centres of ossification.

FIG. 15.

The humerus has seven centres of ossification. There is one for the shaft. About the second year after birth the centre for the head appears; and about the third year, the centre of the tuberosities. About the end of the fifth year, the centres for the head and tuberosities have coalesced, so as to form a large epiphysis on the top of the shaft. It is necessary to remember that this epiphysis includes the tuberosities (as shown in the adjoining wood-cut, fig. 15). On the inner side, the line of junction runs close to the cartilage on the head of the bone: therefore, in the event of separation, the shoulder joint would certainly be implicated. The epiphysis does not unite with the shaft till Epiphysis of the 21st year; so that up to that age it is liable to be separated from the shaft by violence, as we often see in

the head of the humerus.

practice. About the beginning of the third year ossification of the lower end commences by a fourth centre in the lesser head. About the fifth year, a fifth centre appears in the internal condyle. About the twelfth year, a sixth centre appears in the great sweep of the trochlea; and, lastly, about the fourteenth year, the seventh centre appears in the external condyle. At the close of the sixteenth year the lower end has completely ossified, and then unites to the shaft. A separation of the lower epiphysis of the humerus is by no means an infrequent accident in children. The lower fragment is carried backwards with the bones of the fore-arm, so as to cause considerable displacement.

It is interesting to remark, that the epiphysis of the upper end, though it is the first to ossify, yet remains separate from the shaft about three or four years longer than that of the lower end. This is in accordance with the rule, that, of the two epiphyses of a long bone, that towards which the nutrient artery of the marrow runs is always the first to unite with the shaft. Remember that the nutrient arteries of the marrow of the bones of the upper extremity run towards the elbow. In the bones of the lower extremity, they run from the knee.

THE RADIUS.

(Plates XXV. and XXVI.)

The radius is the external of the two bones of the fore-arm, and is so called from its resemblance to the spoke of a wheel. In learning this bone, keep in mind that both its ends are constructed so as to rotate upon the ulna, and admit of the pronation and supination of the hand. The lower end of the radius is much larger than the upper, because it is the chief support of the hand: and since the radius receives all shocks from the hand, it is more liable to be broken than the ulna.

Like the humerus, the radius and ulna are both levers of the third order, as seen in the cut, fig. 16. The fulcrum F is at the elbow jointthe weight W is the fore-arm-the power P is the insertion of the biceps. The biceps will act to the greatest advantage when the arm is bent to a right angle, because the power acts at a right angle to the lever.

HEAD, neck, and tubercle.

The upper end of the radius is called the "head:" it has a shallow circular cup, which articulates (when the fore-arm is bent) with the lesser head of the humerus. Observe that the head has a smooth circular border, which is adapted to rotate in the lesser sigmoid cavity of the ulna. This rotation of the radius can be distinctly felt below the external condyle of the humerus in a natural depression of the skin which exists during life: we mention this because it is of use in determining the existence of fracture. Below the head is the constricted part termed the "neck;" and below this is the "tubercle" which gives insertion to the tendon of the "biceps." Notice that this tubercle projects on the inner side of the bone, so that the biceps can supinate, as well as bend the fore-arm.

SHAFT.

Respecting the "shaft," we observe that its outer side is thick and rounded; and that from

slightly arched outwards, and for two reasons-1, because it increases the breadth of the fore-arm; 2, because it gives more power to the "pronator teres." The bones are furthest apart when the hand is placed vertically: hence, fractures of the fore-arm are put up with the hand vertical, that there may be less risk of the opposite bones uniting.

On the front surface of the shaft there is a blunt ridge leading from the tubercle obliquely towards the outer side of the bone.