THE BREAST. AND AXILLA 25 



lactiferous ducts. Extensive changes occur during the seventh 

 and the ninth months. The lobes derived from the ectodermal 

 buds subdivide to form lobules, which, at their growing ends, 

 invade the surrounding connective tissue and fat, thus breaking 

 up the mesodermal stroma into the interlobular septa and 

 fibrous framework of the corpus mammae. At the same time 

 the whole ectodermal mass becomes canaliculised and gives 

 rise to a system of ducts and alveoli, while the depressed area 

 becomes evaginated on the surface to form the nipple. During 

 the latter part of fcetal life the ampullae develop in the lactiferous 

 ducts, which open on the apex of the nipple. 



At puberty, the size of the gland increases, owing to an 

 increase in the parenchyma ; during pregnancy, the glandular 

 tissue proliferates, and the mamma reaches its full development ; 

 at the menopause, involution occurs in the more recently 

 developed portions. 



The Mammary Gland possesses no capsule ; it consists of 

 a central portion and of peripheral branching processes which 

 radiate into the surrounding paramammary fat (Stiles). The 

 superficial fascia, which covers it, sends down fibrous processes, 

 called the ligaments of 'Cooper, to join the connective tissue septa 

 which ramify throughout the gland. Prolongations of the 

 parenchyma of the gland are found in the ligaments of Cooper, 

 in the loose retro-mammary tissue, and sometimes even in the 

 intervals between the fasciculi of the pectoralis major. When 

 the ligaments of Cooper are invaded by malignant disease, 

 they become shorter and cause dimpling of the skin, which, on 

 this account, is no longer freely movable over the breast. 



The breast rests upon the pectoral fascia and extends from 

 the second rib above to the sixth costal cartilage below. At 

 the level of the fourth rib it extends horizontally from the 

 lateral border of the sternum to the fifth rib in the mid-axillary 

 line (Stiles). Its medial half rests, above, upon the pectoralis 

 major, and, below, on the aponeurosis of the external oblique 

 where it covers the upper part of the rectus abdominis. Its 

 lateral half lies upon the pectoralis major above, and on the 

 serratus anterior (s. magnus) and the external oblique (digitations 

 of origin) below. Spence's axillary tail is a narrow portion of 

 the gland, which reaches up under cover of the pectoralis major 

 as far as the third rib. 



The arterial supply of the mammary gland is derived from 

 the lateral (long) thoracic (p. 31) and the anterior perforating 



