1338 



THE URO-GENITAL SYSTEM. 



while the cells of the lining epithelium, which are now small and glandular, do 

 not contain fat globules. 



The ducts, or ductus lactiferi, passing towards the nipple, become enlarged 

 to form small spindle-shaped dilatations, called ampullae, or sinus lactiferi; then 

 becoming once more constricted, each duct passes, without communicating with its 

 neighbours, to the summit of the nipple, where it opens. 



In the male subject the various parts of the mamma are represented in a 

 vestigial condition. 



The presence of milk-glands is characteristic of the class mammalia, and the 



number of pairs of glands in each group 

 of animals bears some relation to the 

 number of young usually produced at each 

 birth. 



Processes radiating out 

 from the corpus mammae 



Ampulla 

 Ductus lactiferi 



Fat lobule 



Variations. Asymmetry in the development 

 of the mammae is very common the left mamma 

 being very often larger than the right. Absence 

 of one or both mammae is a very rare abnorm- 

 ality, which may or may not be associated with 

 absence of the nipples. When one nipple only 

 is present it is usually the left. The presence of 

 supernumerary glands or nipples is not very un- 

 common, and a large number of examples are 

 recorded. The term polymasty has been applied 

 to cases in which more than the normal number 

 of mammae are present, and polythely to those 

 in which additional glands, in a vestigial 

 condition, are represented by accessory nipples. 

 Usually the accessory glands, or nipples, are pre- 

 sent on the anterior aspect of the thorax, and in 

 most instances they occur below and a little to 

 the medial side of the normal site. When the 

 abnormal glands are found above the normal site 

 they generally lie further from the median plane. 

 Much more rarely accessory glands have been 

 found on the abdomen, in the axilla, or in some 

 other situation, including even the dorsal aspect 

 of the trunk. As many as three extra pairs of 

 mammae have been found in the same individual, 

 and cases in which the probable representatives 

 FIG. 1052. SECTION THROUGH A MAMMARY GLAND, of mammary glands were even more numerous 

 Prepared after immersion in nitric acid as recom- have been recorded. Asymmetry is very common 

 mended by Mr. Harold Stiles. (D.J. Cunningham.) in these abnormal structures. It is interesting 



to note that examples of polymasty and polythely 



occur in the male rather more frequently than in the female. In some women the accessory 

 breasts have yielded milk during lactation ; in most cases the abnormal organs are very 

 rudimentary, and represented only by a minute nipple or pigmented areola. These cases of poly- 

 masty and polythely are supposed to represent a reversion to an ancestral condition, in which 

 more than two mammary glands were normally present, and in which probably many young were 

 produced at each birth. In this connexion it is interesting to observe that usually the accessory 

 glands occur in positions normally occupied by mammae in lower animals. In the course of the 

 development of the mammae in man, specialised areas of the epidermis, similar to those 

 which give origin to the mammae, have been observed both superior and inferior to the region 

 in which the adult mammae are developed. These areas appear to be present normally, 

 but in most cases they disappear at an early stage in the history of the embryo. In some other 

 mammals rudimentary mammae may occur, as, for instance, in lemurs and in some cows. 



A slight functional activity of the mammary glands of the male at birth and about the time 

 of puberty is stated to be. not a very uncommon occurrence. 



Vessels and Nerves of the Mamma. The breast receives its arterial supply from the per- 

 forating branches of the internal mammary artery and from the external mammary branches of the 

 lateral thoracic. Additional supply is sometimes derived from some of the intercostal vessels. 

 The veins coming from the gland pour their blood into the axillary and internal mammary 

 veins. Some small superficial veins from the breast join tributaries of the external jugular. 



The lymph vessels of the breast are very numerous, and form extensive lymph spaces round 

 the alveoli of the gland. These freely anastomose with the lymph vessels of the skin and more 

 especially with the vessels of a very large anastomotic circle deep to the skin of the nipple. The 

 lymph vessels coming from the deep parts of the mamma for the most part join the lymph 

 glands of the axilla. They first run directly towards the deep surface of the breast, where they 

 enter the fascial lymph vessels contained in,* or lying deep to, the fascia of the pectoralis major. 

 These fascial vessels end for the most part in the axillary glands. It is important to remember 



