ARM. 



217 



of the cutaneous nerves of the aim and the 

 superficial veins and absorbents lie imbedded 

 in it: thus the cephalic vein and twigs of the 

 external cutaneous nerve appear along the 

 outer edge of the arm, and along the inner 

 edge are found the internal cutaneous nerve, 

 the brachial branches of the second and third 

 intercostal nerves, the cutaneous nerve which 

 arises from the ulnar high in the axilla, the 

 basilic vein, and a few lymphatic glands, 

 which lie at from one to three inches above 

 the internal condyle. 



Aponeurosis. Beneath the subcutaneous 

 layer of cellular tissue lies the aponeurosis or 

 fascia, which invests the muscles and the deep- 

 seated vessels and nerves of the arm : this 

 fascia commences above at the superior attach- 

 ment of the deltoid muscle ; externally and 

 internally it is continuous with the fascia, 

 which extends over the axillary space; descend- 

 ing along the arm it is strengthened by ex- 

 pansions which it receives from the tendons 

 of the deltoid, pectoralis major, and coraco- 

 brachialis in front ; and behind it derives an 

 accession of strength from the aponeurosis 

 which covers the infra-spinatus and teres minor, 

 and from the tendons of the latissimus dorsi 

 and teres major. At the lower part of the arm 

 the fascia is attached to the condyles of the 

 humerus ; laterally and posteriorly it is at- 

 tached to the olecranon, on either side of 

 which it is continuous with the fascia on the 

 posterior surface of the fore-arm. In front of 

 the elbow this fascia receives a fasciculus of 

 fibres from the tendon of the biceps, and 

 becomes continuous with the fascia covering 

 the anterior surface of the fore-arm. The 

 fascia of the arm varies in strength in different 

 parts ; it is very indistinct over the deltoid, 

 thin but very fibrous on the posterior surface 

 of the arm where it covers the triceps ; it is 

 much stronger over the biceps, and the thickest 

 portion of it is found along the inner edge of the 

 arm, where it covers the brachial artery and its 

 accompanying veins and nerves. A strong 

 aponeurotic septum passes in from the fascia 

 of the arm to each of the lateral ridges of the 

 humerus ; these septa are called intermuscular 

 ligaments, and, together with the humerus, 

 divide the space included within the general 

 fascia into an anterior and a posterior sheath ; 

 the external intermuscular ligament extends 

 from the insertion of the deltoid to the external 

 condyle ; the internal extends from the inser- 

 tion of the coraco-brachialis to the internal 

 condyle. Both intermuscular ligaments are 

 narrowest above, and grow broader as they 

 approach the condyles : their surfaces give at- 

 tachment to fibres of the triceps posteriorly 

 and to the brachiaeus anticus, supinator radii 

 longus, and extensor carpi radialis anteriorly. 

 The posterior sheath,formed as above described, 

 is chiefly occupied by the triceps muscle, be- 

 neath which, in the spiral groove on the pos- 

 terior surface of the humerus, lie the musculo- 

 spiral or radial nerve and the superior pro- 

 funda artery : this nerve and the anterior or 

 musculo-spiral branch of the superior pro- 

 funda artery perforate the external inter- 

 muscular ligament and enter the anterior 



sheath of the arm to get between the brachieeus 

 anticus and supinator radii longus, while the 

 posterior branch of the profunda descends 

 within the v posterior sheath to the back part 

 of the external condyle ; the ulnar nerve and 

 the inferior profunda artery enter this posterior 

 sheath together at its internal side, about the 

 middle of the arm, and descend within it to 

 the back of the internal condyle. A considerable 

 branch of the brachial artery, the ramus anas- 

 tomoticus, perforates the internal intermuscular 

 ligament above the internal condyle, and enters 

 the lower part of the posterior brachial sheath. 

 The anterior sheath of the arm contains the 

 biceps, coraco-brachialis, brachiaeus anticus, and 

 the origins of the long supinator and long 

 radial extensor muscles; the external cutane- 

 ous nerve traverses this sheath, perforating the 

 coraco-brachialis above, and descending ob- 

 liquely outwards between the brachiaeus anticus 

 and the biceps it gets to the outer side of the 

 latter, between the tendon of which and the 

 supinator radii longus it pursues its course to 

 the fore-arm ; the radial nerve and the branch 

 of the superior profunda artery accompanying 

 it are to be found in the lower and external 

 part of the anterior sheath, which they enter 

 as above described : these lie deep between 

 the brachianis anticus and supinator longus. 

 Along the internal side of this anterior sheath, 

 through its whole extent, run the brachial 

 artery, and its two venae comites included in a 

 sheath proper to them, and accompanied by 

 the median nerve, which has very important 

 relations to these vessels : this nerve is external 

 to the artery above, crosses it in the middle 

 of the arm, and lies internal to it below. 

 Superiorly the ulnar nerve lies to the inner 

 side of the brachial artery, from which it se- 

 parates to enter the posterior sheath, as already 

 noticed; the internal cutaneous nerve, the 

 cutaneous twig of the ulnar nerve, and the 

 basilic vein for a short part of its course 

 before it enters the brachial vein, also lie within 

 this sheath; and deeply situated in its lower 

 part is the ramus anastomoticus magnus of the 

 brachial artery. 



Developement. In the progressive deve- 

 lopement of the upper extremity in the fetus, 

 the arm is formed subsequently to the hand 

 and fore-arm, and at an earlier period than the 

 shoulder. In men the deltoid is fuller, and the 

 biceps in front and the triceps behind are more 

 prominent than in women : the greater fulness 

 of these two latter muscles, with the smaller 

 quantity of subcutaneous fat, give to the male 

 arm a greater diameter from before backwards 

 than in the transverse direction ; while the 

 more slender character of the muscles and the 

 greater abundance of subcutaneous fat laterally 

 cause the arm of the female to assume a more 

 rounded form. In the course of the brachial 

 artery two trunks are often found to exist, in 

 consequence of a high branching of that vessel, 

 which sometimes occurs even at the lower 

 border of the axilla: the supernumerary branch 

 in such cases is most frequently the radial : 

 in some instances it is the ulnar and less fre- 

 quently the interosseous or median artery of 

 the fore-arm. When this irregularity occurs, the 



