90 TOPOGRAPHIC AND APPLIED ANATOMY. 



the contents of the neck and abdomen, do not correspond with the external boundaries; they 

 are more difficult to determine in the living subject. 



The upper boundary of the thoracic space in the erect position and during expiration lies 

 in a horizontal plane which passes through a point four centimeters above the middle of the 

 upper margin of the sternum. This plane passes through the intervertebral disc betw r een the 

 last cervical and the first dorsal vertebra. It is about two centimeters above the center of the 

 clavicle, so that the physician may examine a portion of the thoracic contents above this bone. 



The lower boundary of the thoracic space is formed by the diaphragm, the arched dome 

 of which, during expiration, is at the level of the fourth intercostal space in the right mammary 

 line and a fingerbreadth lower in the left mammary line at the upper margin of the fifth rib. 



The physician, as well as the anatomist, needs certain definite vertical and horizontal lines 

 for the purpose of defining the positions of the organs of the thoracic cavity in health and in 

 disease. 



The vertical lines are : The mammary line, passing through the nipple [the position of the 

 nipple is so variable that the mammary line should be abandoned in favor of the mid-clavicular 

 line; the latter starts from a fixed and easily determined point, passes usually slightly internal 

 to the nipple, and in normal subjects is continuous with the Poupart perpendicular drawn from 

 the mid-point between the symphysis pubis and the anterior superior spinous process and used 

 by many writers in delimiting the abdominal regions. ED.]; the sternal line, along the margin of 

 the sternum ; the parasternal line, midway between the mammary and sternal lines ; and the axillary 

 line, which passes downward from the highest point of the axillary fossa (also known as the middle 

 axillary line). The anterior axillary line passes vertically downward from the point at which 

 there appears the prominence caused by the lower margin of the pectoralis major as it leaves 

 the thoracic wall; the posterior axillary line extends vertically downward from the correspond- 

 ing point of the latissimus dorsi. The costoclavicular line is drawn from the sternoclavicular 

 articulation to the end of the eleventh rib and is employed to determine the normal position of 

 the spleen. The scapular line passes through the inferior angle of the scapula. These lines 

 are supplemented by the anterior and posterior median lines. 



The horizontal lines are furnished by the intercostal spaces. At the upper portion of the 

 sternum, the sternal angle (angle of Ludwig) may be seen and felt as a transverse elevation. It 

 corresponds to the synchondrosis between the manubrium and the gladiolus and to the attach- 

 ment of the second costal cartilage. In this manner the second intercostal space may be easily 

 located and the remaining intercostal spaces may be defined by firm palpation from above down- 

 ward and backward. The importance of these localizing lines is clear; for example, the apex 

 of the normal heart (apex-beat) is situated in the fifth intercostal space between the mammary 

 and the parasternal lines. The third intercostal space is the broadest, then follow the first and 

 the second; all of the other intercostal spaces are narrower, the last one being the narrowest. 

 The intercostal spaces are broader anteriorly than posteriorly, for which reason penetrating 

 injuries from behind (a gunshot wound, for example) are more frequently complicated with 

 injuries to the ribs than are similar wounds from in front. 



[Anteriorly the thorax is divided into the following regions: Supraclavicular, that portion 

 above the clavicle; infraclavicular, between the clavicle and the third rib; mammary, between 



