SURGICAL ANATOMY OF THE UPPER EXTREMITY. 499 



oblique elongated eminence is seen, caused by the emergence of two of the extensors of the 

 thumb from their deep origin at the back of the forearm. This eminence, full above and be- 

 coming flattened out and partially subdivided below, runs downward and outward over the back 

 and outer surface of the radius to the outer side of the wrist-joint, where it forms a ridge, 

 especially marked when the thumb is extended, which passes onward to the posterior aspect of 

 the thumb. The tendons of most of the extensor muscles are to be seen and felt at the level 

 of the wrist-joint. Most externally are the tendons of the Extensor ossis metacarpi pollicis and 

 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 princjpally 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 Palmar!.* ////> 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 Lumliric'tl //(//.W-.* 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 the strong central part of the 

 palmar fascia. Here we have some fiirrows, 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 to the head of the metacarpal bone 

 of the index finger. A second passes inward, with a slight inclination upward, from the termi- 

 nation of the first to the ulnar side of the hand. A third runs 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 characteristics less than elsewhere. 

 In spite of this hardness and density, the skin of the palm is exceedingly sensitive and very 

 vax-ular. 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 phalantres it is thrown into numerous parallel ridges in consequence of the 

 arrangement of the papillae in it. The superficial 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 pro- 

 duce elongate'! swellings between the metacarpal bones. The first dorsal interosseous (Abductor 

 indicis i. when the thumb is closely adducted to the hand, forms a prominent fusiform bulging; 

 the other interossei are not so marked. 



SURGICAL ANATOMY OF THE UPPER EXTREMITY. 



The student, having 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, I 

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



Fracture of the middle of the clavicle (Fig. 319) 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, owing to the displacement backward of its 

 inner end. The whole outer fragment is somewhat depressed. 



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 Subclavius, the 

 Pectoralis minor and major, and the Latissimus dorsi ; backward, with consequent rotation of 

 the outer end of the outer frainnent forward by the Pectoral muscles. 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 fragment 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-mastoid, or by 

 the inner end of the outer fragment getting below and behind it. The causes of displacement 

 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. 



