SURFACE FORM OF THE UPPER EXTREMITY 497 



at the lower part of the arm, the Brachialis anticus is discernible. On the outer side it forms 

 a narrow eminence which extends some distance up the arm along the border of the Biceps. 

 On the inner side it shows itself only as a little fulness just above the elbow. On the back of 

 the arm the long head of the Triceps may be seen as a longitudinal eminence emerging from 

 under cover of the Deltoid, and gradually merging into the longitudinal flattened plane of the 

 tendon of the muscle on the lower part of the back of the arm. The tendon of insertion of the 

 muscle extends about half-way up the back of the arm, where it forms an elongated flattened 

 plane when the muscle is in action. Under similar conditions the surface forms produced by 

 the three heads of the muscle are well seen. 



On the anterior aspect of the elbow are to be seen two muscular elevations, one on each 

 side, separated above and converging below so as to form a triangular space. Of these, the 

 inner elevation, consisting of the Flexors and Pronators, forms the prominence along the inner 

 side and front of the forearm. It is a fusiform mass, pointed above at the internal condvle 

 and gradually tapering off below. The Pronator teres, the innermost muscle of the group, 

 forms the boundary of the triangular space at the bend of the elbow. It is shorter, less 

 prominent, and more oblique than the outer boundary. The most prominent part of the 

 eminence is produced by the Flexor carpi radian's, the muscle next in order on the inner 

 side of the preceding one. It forms a rounded prominence above, and can be traced down- 

 ward to its tendon, which can be felt lying on the front of the wrist, nearer to the radial 

 than to the ulnar border, and to the inner side of the radial artery. The Palmaris longus pre- 

 sents no surface marking above, but below is the most prominent tendon on the front of the 

 wri.st, standing out, when the muscle is in action, as a sharp, tense cord beneath the skin. The 

 Flexor sublimis digitorum does not directly influence surface form. The position of its four 

 tendons on the front of the lower part of the forearm is indicated by an elongated depression 

 between the tendons of the Palmaris longus and the Flexor carpi ulnaris. The Flexor carpi 

 ulnaris occupies a small part of the posterior surface of the forearm, and is separated from the 

 Extensor and Supinator group, which occupies the greater part of this surface, by the ulnar 

 furrow, produced by the subcutaneous posterior border of the ulna. Its tendon can be perceived 

 along the ulnar border of the front of the forearm, and is most marked when the hand is flexed 

 and adducted. The deep muscles of the front of the forearm have no direct influence on sur- 

 face form. The external group of muscles of the forearm, consisting of the Extensors and Supi- 

 nators, occupy the outer and a considerable portion of the posterior surface of this region. It 

 has a fusiform outline, which is altogether on a higher level than the Pronator teres and Flexors. 

 Its apex emerges from between the Triceps and Brachialis anticus muscles some distance above 

 the elbo\v-joint, and acquires its greatest breadth opposite the external condvle, and thence 

 gradually shades off into a flattened surface. About the middle of the forearm it divides into 

 two longitudinal eminences which diverge from each other, leaving a triangular interval between 

 them. The outer of these two groups of muscles consists of the Brachioradialis and the Extensores 

 carpi radialis longior et brevior, which form a longitudinal eminence descending from the external 

 condylar ridge in the direction of the styloid process of the radius. The other and more pos- 

 terior group consists of the Extensor communis digitorum, the Extensor minimi digiti, and 

 the Extensor carpi ulnaris. It commences above as a tapering form at the external condyle 

 of the humerus, and is separated behind at its upper part from the Anconeus by a well-marked 

 furrow, and below, from the Pronato-flexor mass, by the ulnar furrow. In the triangular 

 interval left between these two groups the Extensors of the thumb and index finger are seen. 

 The only two muscles of this region which require special mention as independently influencing 

 surface form are the Brachioradialis and the Anconeus. The inner border of the Brachio- 

 radialis forms the outer boundary of the triangular space at the bend of the elbow. It com- 

 mences as a rounded border above the condyle, and is longer, less oblique, and more prominent 

 than the inner boundary. Lower down, the muscle forms a full fleshy mass on the outer side of 

 the upper part of the forearm, and below tapers into a tendon, which may be traced down to 

 the styloid process of the radius. The Anconeus presents a well-marked and characteristic 

 surface form in the shape of a triangular, slightly elevated surface, immediately external to the 

 subcutaneous posterior surface of the olecranon, and differentiated from the common Extensor 

 group by a well-marked oblique longitudinal depression. The upper angle of the triangle 

 corresponds to the external condyle, and is marked by a depression or dimple in this situation. 

 In the interval caused by the divergence from each other of the two groups of muscles into which 

 the Extensor and Supinator group is divided at the lower part of the forearm an oblique elon- 

 gated 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 becoming flattened 

 out and partially subdivided below, runs downward and outward over the back and outer sur- 

 face 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 



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