AXILLARY SPACE 35 



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 

 diverge to form a thin muscular sheet, which is inserted into 

 the anterior lip of the vertebral border 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. 

 These 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 upper extremity. 



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 disinfectant 

 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 this position for five days, and during the first two of these the dis- 

 sector of the upper extremity must examine the structures which connect 

 the limb with the posterior aspect of the trunk. 



Surface Anatomy. In the middle line of the back there 

 is little difficulty in recognising the tips of the spinous processes 

 of the vertebrae. These follow each other in consecutive 

 order, and it may be observed, when the finger is passed 

 over them, that all of them do not lie in the medial plane : 

 some may be deflected, in a slight degree, to one side or the 

 other. The spines of the vertebrae are the only parts of the 

 vertebral column which come to the surface ; they alone 

 yield direct information, by touch, to the surgeon as to the 

 condition of the spine. At the lower end of the neck, the 

 spine of the seventh cervical vertebra (vertebra prominens) 

 makes a visible projection ; and the spines of the first 

 two thoracic vertebras are likewise very prominent. As 

 a rule, the most evident of the three is that of the first 

 thoracic vertebra. At a lower level, in subjects of good 

 muscular development, a median furrow is produced by the 

 prominence of the sacrospinalis muscle on each side, and 



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