224 DISSECTION OF THE UPPER LIMB. 



CHAPTEE III. 



DISSECTION OF THE UPPER LIMB. 



SECTION I. 



THE WALL OF THE THORAX AND THE AXILLA. 



THE parts included in this section, viz., the wall of the chest and the 

 axilla, are to be learnt within a fixed time, in order that the examination 

 of the thorax may be undertaken. Whilst the dissection of the thorax 

 is in progress, the student will have to discontinue his labors on the upper 

 limb ; but, on the completion of that cavity, he must be ready to begin 

 the part of the Back that belongs to him. 



Position. Whilst the body lies on the Back, the thorax is to be raised 

 to a convenient height by a block ; and the arm, being slightly rotated 

 outwards, is to be placed at a right angle to the trunk. 



Directions. Before the dissection is entered on, attention should be 

 given to the depressions on the surface, to the prominences of muscles, 

 and to the projections of the bones ; because these serve as guides to the 

 position of parts beneath the skin. 



Surface-marking. Between the arm and the chest is the hollow of 

 the arm-pit, in which the large vessels and nerves of the limb are lodged. 

 The extent of this hollow may be seen to vary much with the position of 

 the limb to the trunk ; for in proportion as the arm is elevated, the fore 

 and hinder boundaries are carried upwards and rendered tense, and the 

 depth of the space is diminished. In this spot the skin is of a dark color, 

 and is furnished with hairs and large sweat glands. 



If the arm is forcibly raised and moved in different directions, whilst 

 the fingers of one hand are placed in the arm-pit, the head of the humerus 

 may be recognized. 



On the outer side of the limb is the prominence of the shoulder ; and 

 immediately above it is an osseous arch, which is formed internally by the 

 clavicle, and externally by the spine and the acromion process of the 

 scapula. Continued downwards from about the middle of the clavicle, is 

 a slight depression between the pectoral and deltoid muscles, in which the 

 coracoid process can be felt near that bone. A second groove, extending 

 outwards from the sternal end of the clavicle, corresponds with the inter- 

 val between the clavicular and sternal origin of the great pectoral muscle. 



Along the front of the arm is the prominence of the biceps muscle ; and 

 on each side of that eminence is a groove, which subsides inferiorly in a 

 depression in front of the elbow-joint. The inner of the two grooves, the 

 deepest, indicates the position of the brachial vessels. 



If the elbow joint be semiflexed, the prominences of the outer and inner 

 condyles of the humerus will be rendered evident, especially the inner. 



