498 THE MUSCLES AND FASCIA 



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, so far as regards surface form, in producing 

 the thenar and hypothenar eminences, and individually are not to be distinguished, on the sur- 

 face, 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, 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 oveY the hypothenar 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 the strong central part of the palmar fascia. 

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

 carpal bones. When the thumb is adducted the First dorsal interosseous forms a prominent 

 fusiform bulging; the other Interossei are not so marked. 



The skin over the inner side and front of the forearm is thin, smooth, and sensitive; it 

 contains few hairs and many sweat glands. Over the outer side and back of the arm and 

 forearm it is thicker, denser, and less sensitive, and contains more hairs and fewer sweat 

 glands. Over the olecranon the cuticle is thick and rough; the skin is loosely connected 

 to the underlying tissues and becomes transversely wrinkled when the forearm is extended. 

 At the front of the wrist the skin presents three transverse furrows, which correspond from 

 above downward to the position of the styloid process of the ulna, the wrist-joint, and the 

 midcarpal joint, respectively. 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 by 

 a thick layer of cuticle. The skin in the thenar region presents these characteristic's less 

 than elsewhere. In spite of this hardness and density, the skin of the palm is exceedingly 

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

 found in this region. It is tied down by fibrous bands along the lines of flexion of the digits, 

 producing certain furrows of a permanent character. One of these, starting from about the 

 tubercle of the scaphoid, curves around the thenar eminence, and ends on the radial border of 

 the hand, a little above the metacarpophalangeal joint of the index finger. It corresponds to 

 the outer border of the central portion of the palmar fascia, and is produced by the movements 

 of the thumb at the carpometacarpal joint. A second line begins at the end of the first and 

 extends obliquely across the palm upward and inward, to the ulnar margin about the middle 

 of the fifth metacarpal bone. A third commences at the ulnar border of the hand about an 

 inch below the termination of the second and extends outward across the palm over the heads of 

 the third, fourth, and fifth metacarpal bones. These last two lines are caused by the flexion of 

 the fingers at the metacarpophalangeal joints. 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, distinctive and permanent patterns, which may be used for purposes of identifi- 

 cation. The superficial fascia in the palm is made up of dense fibrofatty tissue. This tissue 

 binds down the skin so firmly to the deep palmar fascia that very little movement is permitted 

 between the two. 



APPLIED 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 action 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. 372) 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 

 depressed. The deformity is described by saying that the shoulder goes downward, forward, 

 and inward. 



