AXILLARY SPACE 47 



the serratus anterior, before it unites with the other part of 

 the nerve. The entire nerve can be followed to the lower 

 part of the serratus anterior, giving twigs to each of its 

 digitations. 



M. Serratus Anterior (O.T. Serratus Magnus). The 

 serratus anterior arises by fleshy digitations from the upper 

 eight ribs, about midway between their angles and cartilages. 

 The slips are arranged on the chest wall so as to present a 

 gentle curve convex forwards. The lower three interdigitate 

 with the external oblique muscle of the abdomen. The 

 serratus anterior is inserted into the entire length of the 

 anterior lip of the vertebral margin of the scapula, and it falls 

 naturally into three parts, (a) The upper part^ composed of 

 the large first digitation alone, arises from the first and second 

 ribs, and from a tendinous arch between them. The fibres 

 converge, to be inserted into a somewhat triangular surface on 

 the costal aspect of the medial angle of the scapula, (b) The 

 middle part consists of two digitations which take origin from 

 the second and third ribs. The upper slip is very broad, and 

 springs from the lower border of the second rib. The fibres 

 of the middle part diverge to form a thin muscular sheet, 

 which is inserted into the anterior lip of the vertebral margin 

 of the scapula, between the insertions of the upper and lower 

 portions. (c] The lower part is formed by the remaining 

 digitations of the muscle. They converge to form a thick 

 mass, which is inserted into a rough surface upon the costal 

 aspect of the inferior angle of the scapula. The deep surface 

 of the serratus anterior is in contact with the chest wall. 

 It is the most powerful protractor of the whole upper 

 extremity. 



DISSECTION OF THE BACK. 



Dissection. At the end of the fifth day, after the dissector 

 has examined the serratus anterior and carefully revised the 

 contents of the axilla, he must replace the clavicle, pack the 

 axilla with tow or rags steeped with preservative solution and 

 fix the skin flaps to the wall of the thorax with a few stitches. 

 When he returns on the sixth day he will find that the body has 

 been placed upon its face, with blocks supporting the chest and 

 the pelvis. It will remain in that position for five days, and 

 during the first two of those the dissector of the upper extremity 

 must examine the structures which connect the limb with the 

 posterior aspect of the trunk. 



