PARTS ON FRONT OF THORAX. 225 



Below the outer condyle, and separated from it by a slight interval, the 

 head of the radius projects ; it may be recognized by rotating the bone, 

 the fingers at the same time being placed over it. At the back of the 

 articulation is the prominence of the olecranon. 



Dissection. As the first step in the dissection, raise the skin from the 

 side of the chest and the arm-pit, over the great pectoral muscle and the 

 hollow of the axilla, by means of the following incisions : One is to be 

 made along the middle of the sternum. A second, carried along the cla- 

 vicle for the inner two-thirds of that bone, is to be continued down the 

 front of the arm rather beyond the anterior fold of the arm-pit, and then 

 to be turned across the inner surface of the arm as far as the hinder fold 

 of the axilla. From the xiphoid cartilage a third cut is to be directed 

 outwards over the side of the chest, as far back as to a level with the pos- 

 terior fold of the arm-pit. 



The flap of skin now marked out should be reflected outwards beyond 

 the axilla ; but it should be left attached to the body, in order that it 

 may be used afterwards for the preservation of the part. 



The subcutaneous fatty layer of the thorax resembles the same structure 

 in other parts of the body; but in this region it does not contain much fat. 



Beneath the subcutaneous layer is a deeper and stronger special fascia 

 which closely invests the muscles, and is continuous with the deep fascia 

 of the arm. It is thin on the side of the chest, but becomes much thicker 

 where it is stretched across the axilla. An incision through it, over the 

 arm-pit, will render evident its increased strength in this situation, and 

 the casing it gives to the muscles bounding the axilla ; and if the fore 

 finger be introduced through the opening, some idea will be gained of its 

 capability of confining an abscess in that hollow. 



Dissection. The cutaneous nerves of the side of the chest are to be 

 next sought. At the spots where they are to be found they are placed 

 beneath the fat, so that the student must cut through it ; and those on the 

 clavicle lie also beneath the platysma muscle. Small vessels will indicate 

 the position of the nerves. 



Some of them (from the cervical plexus) cross the clavicle at the middle, 

 and the inner part. Others (anterior cutaneous of the thorax) appear at 

 the side of the sternum one from each intercostal space. And the rest 

 (lateral cutaneous of the thorax) should be looked for along the side of the 

 chest, about one inch below the anterior fold of the axilla, there being one 

 from each intercostal space except the first : as the last-mentioned nerves 

 pierce the wall of the thorax, they divide into an anterior and a posterior 

 piece. 



The posterior pieces of the highest two nerves are larger than the rest. 

 They are to be followed across the arm-pit, and a junction is to be found 

 there with a branch (nerve of Wrisberg) of the brachial plexus. 



Cutaneous nerves of the cervical plexus. These cross the clavicle and 

 are distributed to the integuments over the pectoral muscle. The most 

 internal branch (sternal) lies near the inner end of the bone, and reaches 

 but a short distance below it. Other branches (clavicular), two or more 

 in number and larger in size, cross the centre of the clavicle and extend 

 to near the lower border of the pectoralis major ; they join one or more of 

 the anterior cutaneous nerves of the thorax. 



The cutaneous nerves of the thorax are derived from the trunks of the 

 intercostal nerves between, the ribs (fig. 69). Of these there are two 

 sets : One set, lateral cutaneous nerves of the thorax, arise from the 

 15 



