THE BACK AND SPINE. 



477 



THE BACK AND SPINE. 



SURFACE ANATOMY. 



On examining the back of a person standing- upright a median fiirrow is seen 

 (Fig. 477). In the bottom of this the tips of the spinous processes can be felt. If the 

 back is bent these processes can be distinctly seen; they should form a straight line. 

 The second cervical spine can be felt by deep pressure in a relaxed neck. The sixth 

 is usually the first one visible and the seventh cervical and first dorsal are very promi- 

 nent, often the latter the more so. The furrow ends abruptly at the top of the sacrum. 

 From this point down to near the top of the gluteal fold is a triangular space with 

 its base above and apex downward. Its apex marks the third sacral spine, and just 

 above this latter, opposite the second sacral spine, on each side can be felt the posterior 

 superior iliac spines. The erector spina (sacrolumbalis) muscles form elevations on 

 each side of the furrow, most marked in the lumbar region. In muscular people the 

 erector spinse is seen to consist of two parts : an inner longissimus dorsi muscle, and 

 an outer iliocostalis. Above, the projections of the scapulce are visible. If the arms 



Seventh cervical 

 Outer end of clavicle 

 Acromion process 



Root of spine of scapula 



Median furrow 

 Angle of scapula 



Depression along outer 

 edge of erector spinae 



Mass of erector spinae 

 muscles 



Posterior superior 

 spine of ilium 



Third sacral spine 



FIG. 477. Surface anatomy of the back. 



are by the sides the posterior border of the scapula is parallel to the median line. 

 The root of the spine of the scapula in a muscular person makes a depression. It is 

 opposite the third dorsal spine or the body of the fourth thoracic vertebra, and marks 

 the upper end of the fissure of the lungs. The spine of the scapula is subcutaneous 

 and can be traced out to the acromion process. The lower angle of the scapula is 

 opposite the upper border of the eighth rib; the upper angle covers the second rib 

 but its tip is level with the first. 



In the lumbar region the erector spinae muscle forms a clearly marked promi- 

 nence. The twelfth rib usually projects beyond its outer edge, which is marked by a 

 depression separating it from the abdominal muscles in front. It is through this 

 depression that operations on the kidney are performed (see page 428). The dis- 

 tance between the twelfth rib and crest of the ilium is usually 6. 25 cm. (2^ in. ) but it 

 may be more and is often less. Just above the middle of the crest of the ilium is 

 Petit' s triangle (page 394); and to the inner side of the lower third of the poste- 



