302 A MANUAL OF ANATOMY 



more) emerge from the deep part of the gland. These pierce the 

 pectoralis major muscle, and terminate in one of the infra-clavicular 

 glands. (3) A third set of lymphatics emerge from about the inner 

 third of the gland. These pierce the pectoralis major muscle near 

 the lateral border of the sternum, the anterior intercostal aponeu- 

 rosis, and the interchondral portions of the internal intercostal 

 muscles, after which they terminate in the internal mammary 

 glands, otherwise known as the anterior intercostal or sternal glands. 



Nerves. — ^These are derived from the supraclavicular branch of 

 the cervical plexus, and the anterior and lateral cutaneous branches 

 of the upper intercostal nerves. 



Accessory mammae are sometimes met with on the upper, lower, 

 and inner outskirts of the main gland, and more rarely in the 

 axilla, or on the upper part of the anterior abdominal wall. 



Structure of the Mamma. — The mammary gland belongs to the class of 

 acino-tubular or compound racemose glands. It consists of — (i) glandular 

 tissue, and (2) a fibrous connective-tissue stroma, which together constitute a 

 firm light red mass, known as the corpus mammce. 



The glandular element is composed of large lobes, varying in number from 

 fifteen to twenty. There is no firm fibrous capsule, such as that possessed by 

 the parotid salivary gland, but the superficial pectoral fascia, within which the 

 mammary gland is embedded, sends inwards fatty processes between the lobes, 

 the supporting fibrous tissue of these processes being continuous with the 

 sustentacular tissue of the gland. Each lobe is tapering in outline, and is 

 provided with its ov.^ duct, the various lobes being disposed in a radiating^ 

 manner from the nipple. ^ 



A mammary lobe, being large, is made up of smaller lobes, and each small' 

 lobe consists of a group of lobules, the structure of which furnishes the key' 

 to the structure of the entire gland. 



A mammary lobule consists of from one to three acini, and these have one- 

 duct in common. This duct is one of the radicles of the main duct of a given 

 mammary lobe. The radicle duct breaks up into two or three somewhat 

 dilated excretory passages, the walls of each of which are convoluted. This 

 convoluted character is due to the fact that the walls are distended into a 

 series of pouches, called alveoli, which beset all parts of the wall of the acinus, 

 including its caecal end, thus giving it somewhat of the appearance of a grape 

 — hence the name acinus. The wall of each alveolus consists of a delicate 

 basement membrane, which is invested by capillary bloodvessels, and lined 

 with cubical or short columnar epithelium. From one to three acini, as: 

 stated, constitute a lobule, and they are consequently appendages of a lobular 

 duct. Contiguous lobular ducts unite and form the duct of a small lobe, and 

 the contiguous ducts of small lobes unite, and form the duct of a large lobe.. 

 The number of main ducts corresponds to the number of main lobes — namely, 

 from fifteen to twenty. They are referred to as the lactiferous or galacto-i 

 phorous ducts. The main lactiferous ducts converge towards the nipple. As 

 they lie beneath the areola, each. duct expands into a somewhat spindle-shaped 

 dilatation, called the ampulla or lactiferous sinus, which serves as a reservoir 

 for the milk during lactation. Thereafter the duct becomes narrow, and 

 having traversed the nipple, it opens upon its summit at the bottom of a 

 small depression or foveola. The orifice of the duct is of smaller size than the 

 excretory tube leading to it. The arrangement of orifices at the summit of 

 the nipple may be compared to the arrangement of the orifices of the excretory 

 tubes of the kidney at the apex of a given Malpighian pyramid. 



The walls of the ducts consist of areolar and elastic tissue, and they are 

 lined with columnar epithelium. The elastic tissue is disposed both longi- 

 tudinally and in a circular manner. 



