1 1 6 Anatomy Applied to Medicine and Suvgeiy. 



ulae (posterior divisions of the same nerves) ; to the neck 

 (supraclavicular) ; down the arm (intercosto-humeral 

 from the intercostal, or through the anterior thor- 

 acics to the brachial plexus) ; while the connection 

 with the sympathetic explains the intimate association be- 

 tween the genital organs and the breast. 



The circumference of the mammary gland is not cir- 

 cular but presents three projections, one towards the ster- 

 num and two towards the axilla one above, and the other 

 below. Occasionally, there exist smaller extensions from 

 the under surface of the gland that pierce the deep fascia 

 and even penetrate the substance of the pectoral muscle. 

 These processes may be left behind, if the pectoralis major 

 be not removed in the operation for mammary cancer and 

 may, therefore, form nuclei for the recurrence of the 

 disease. 3. ^^ external intercostal muscles extend from 

 the tuberosities of the ribs behind, to the costal cartilages 

 in front, and pass obliquely downwards and forwards 

 from the lower border of the rib above, to the upper border 

 of the rib below, and, where these muscles are deficient in 

 front, they are replaced by the anterior intercostal apon- 

 euroses. 4. The internal intercostals, on the other hand, 

 pass downwards and backwards from one rib to the other 

 and extend from the sternum in front to the angles of the 

 ribs behind, and are replaced posteriorly by the posterior 

 intercostal aponeuroses. 



Functions. These intercostal muscles are concerned 

 with respiration and enlarge the chest in its antero-poste- 

 rior diameter by elevating the cartilages and the sternum, 

 and, in its lateral diameter by rotating the individual ribs. 

 5. The intercostal nerves, derived from the dorsal portion 

 of the spinal cord, pass forward between the two planes of 

 intercostal muscles to about the midaxillary line, where 

 they enter the internal muscles and continue onwards in 



