THE MAMMARY GLANDS 



1299 



Development.^The sebaceous glands appear first in the fifth fcctal month as single, rarely 

 double, buds on the anlages of the hair follicles. The distal ends of these enlarge and become 

 lobulated. In these soUd masses of cells lumina for the alveoh and the ducts later are formed, 

 through the fatty degeneration of the central cells. The oily contents of these cells together 

 with the debris and the cast-off surface cells of the epidermis form the vernix caseosa on the sur- 

 face of the foetus. 



D. THE MAMMARY GLANDS 



The mammary glands [mammae] or breasts are modified cutaneous glands. 

 In the male they remain rudimentary and functionless throughout life, but in 

 the female they are functionally closely associated with the reproductive organs 

 since they secrete the milk for the nourishment of the newborn and are subjected 

 to marked changes at puberty, throughout pregnancy, during and after lacta- 

 tion, and after the menopause. 



Fig. 1058. — The Right Mamma of a Girl 18 Years Old. (Modified from Spalteholz.) 



Acromion 



The two mammae (fig. 1058) are situated on the ventral surface of the thorax 

 one on each side of the sternum. As examined from the surface in a well-developed 

 nulliparous female they appear to extend from the second or third rib to the sixth 

 or seventh costal cartilage and from the lateral border of the sternum to beyond 

 the ventral folds of the axillae. Separating the two mammae there is a median 

 unraised area of variable size, the sinus mammarum. 



In shape they are conical or hemispherical, and in consistency somewhat 

 firm and elastic. The size of the two breasts is seldom equal, the left, as a rule 

 being slightly the larger. Each measures from 10 to 13 cm. in diameter being 

 slightly longer in the direction parallel to the lateral border of the pectoralis major 

 muscle. The weight of each gland varies from 140 to 200 grams, or more. 



Each mamma presents for examination a ventral surface and a dorsal surface. 

 The ventral surface is free, covered by skin, smooth and convex. It is continuous 



