SURGICAL ANATOMY OF THE UPPER EXTREMITY. 411 



the Extensor brevis pollicis, forming a vertical ridge over the outer side of the joint from the 

 styloid process of the radius to the thumb. Internal to this is the oblique ridge produced by 

 the tendon of the Extensor longus pollicis, very noticeable when the muscle is in action. The 

 Extensor carpi radialis longior is scarcely to be felt, but the Extensor carpi radialis brevior can 

 be distinctly perceived as a vertical ridge emerging from under the inner border of the tendon 

 of the Extensor longus pollicis, when the hand is forcibly extended at the wrist. Internal to 

 this, again, can be felt the tendons of the Extensor indicis, Extensor communis digitorum, and 

 Extensor minimi digiti ; the latter tendon being separated from those of the common extensor 

 by a slight furrow. The muscles of the hand are principally concerned, as far as regards sur- 

 face-form, in producing the thenar and hypothenar eminences, and individually are not to be 

 distinguished, on the surface, from each other. The Adductor transversus pollicis is, however, 

 an exception to this ; its anterior border gives rise to a ridge across the web of skin connecting 

 the thumb to the rest of the hand. The thenar eminence is much larger and rounder than the 

 hypothenar one, which presents a longer and narrower eminence along the ulnar side of the 

 hand. When the Palmaris brevis is in action it produces a wrinkling of the skin over the hypo- 

 thenar eminence, and a deep dimple on the ulnar border of the hand. The anterior extremities 

 of the Lumbrical muscles help to produce the soft eminences just behind the clefts of the fingers, 

 separated from each other by depressions corresponding to the flexor tendons in their sheaths. 

 Between the thenar and hypothenar eminences, at the wrist-joint, is a slight groove or depression, 

 widening out as it approaches the fingers; beneath this we have th>e strong central part of the 

 palmar fascia. Here we have some furrows, which are pretty constant in their arrangement, 

 and bear some resemblance to the letter M. One of these furrows passes obliquely outward 

 from the groove between the thenar and hypothenar regions near the wrist to the head of the 

 inetacarpal bone of the index finger. A second passes inward, with a slight inclination upward, 

 from the termination of the first to the ulnar side of the hand. A third runs nearly parallel 

 with the second and about three-quarters of an inch below it. Lastly, crossing these two latter 

 furrows, is an oblique furrow parallel with the first. The skin of the palm of the hand differs 

 considerably from that of the forearm. At the wrist it suddenly becomes hard and dense, and 

 covered with a thick layer of cuticle. The skin in the thenar region presents these characteris- 

 tics less than elsewhere. In spite of this hardness and density, the skin of the palm is exceed- 

 ingly sensitive and very vascular. It is destitute of hair, and no sebaceous follicles have been 

 found in this region. Over the fingers the skin again becomes thinner, especially at the flexures 

 of the joints, and over the terminal phalanges it is thrown into numerous ridges in consequence 

 of the arrangement of the papillae in it. These ridges form, in different individuals, dis- 

 tinctive and permanent patterns, which may be used for purposes of identification. The super- 

 ficial fascia in the palm is made up of dense fibro-fatty tissue. This tissue binds down the skin 

 so firmly to the deep palmar fascia that very little movement is permitted between the two. 

 On the back of the hand the Dorsal interossei produce elongated swellings between the meta- 

 carpal bones. The first dorsal interosseous (Abductor indicis), when the thumb is closely ad- 

 ducted to the hand, forms a prominent fusiform bulging ; the other interossei are not so 

 marked. 



SURGICAL ANATOMY OF THE UPPER EXTREMITY. 



The student, haying completed the dissection of the muscles of the upper extremity, should 

 consider the effects likely to be produced by the action of the various muscles in fracture of the 

 bones. 



In considering the actions of the various muscles upon fractures of the upper extremity, the 

 most common forms of injury have been selected both for illustration and description. 



Fracture of the middle of the clavicle (Fig. 246) is always attended with considerable dis- 

 placement; the inner end of the outer fragment is displaced inward and backward, while the 

 outer end of the same fragment is rotated forward. The whole outer fragment is somewhat de- 

 pressed. 



The displacement is produced as follows : inward, by the muscles passing from the chest to 

 the outer fragment of the clavicle, to the scapula, and to the humerus, viz., the Subclayius and 

 the Pectoralis minor, and, to a less extent, the Pectoralis major and the Latissimus dorsi ; back- 

 ward, in consequence of the rotation of the outer fragment. The Serratus magnus causes the 

 scapula to rotate on the wall of the chest ; this carries the acromion and outer end of the outer 

 fragment of the clavicle forward and causes the piece of bone to rotate round a vertical axis 

 through its centre, and so carries the inner end of the outer portion backward. The depression 

 of the whole outer fragment is produced by the weight of the arm and by the contraction of the 

 Deltoid. The outer end of the inner fraginent appears to be elevated, the skin being drawn 

 tensely over it ; this is owing to the depression of the outer fragment, as the inner fragment is 

 usually kept fixed by the costo-clavicular ligament and by the antagonism between the Sterno- 

 mastoid and Pectoralis major muscles. But it may be raised by an unusually strong Sterno-mas- 

 toid, or by the inner end of the outer fragment getting below and behind it. The causes of dis- 

 placement having been ascertained, it is easy to apply the appropriate treatment. The outer 

 fragment is to be drawn outward, and, together with the scapula, raised upward to a level with 

 the inner fragment, and retained in that position. 



