418 STRUCTURE AND SECRETORY ACTIVITY OF MAMMARY GLANDS. 



of the mammary gland at the temperature of the body casein also is formed 

 as a result of a fermentative process, and probably from serum-albumin. This 

 ferment is present in the milk. 



The mammillary areola and the nipple are characterized by pigmentary deposits 

 in the cells of the rete Malpighii (during pregnancy more abundant and of greater 

 extent) and by large papillae in the cutis, some of which contain tactile corpuscles. 

 Numerous unstriated muscle-fibers in the deep layers of the corium and in the 

 subcutaneous tissue (always free from fat) surround the milk-ducts of the nipples 

 and in part also pass longitudinally to the tip of the nipple. The glands of Mont- 

 gomery, about the size of a millet-seed, situated during lactation in the mam- 

 millary areola, are small, nodular, prominent, subcutaneous milk-glands, with 

 a special duct of evacuation at the summit of each nodule. 



Arteries enter the mammary gland from different directions. Their branches 

 do not accompany the glandular ducts. Capillaries arranged in a network sur- 

 round the glandular acini and anastomose by means of small arteries and veins 

 with those of the neighboring vesicles. In the mammillary areola the veins are 

 arranged in the form of rings (circles of Haller) . 



The nerves of the mammary gland arise from the supra-clavicular and the 

 second, fourth and sixth intercostals. They pass in part to the skin of the gland 

 and of the highly sensitive nipple, in part to the vessels, and in part to the 

 unstriated muscle-fibers of the nipple and to the glandular vesicles themselves, in 

 which their mode of termination is, however, as yet unknown. In connection 

 with the investigations of the mammary glands great credit belongs to C. 

 Langer. 



Lymphatics are found close about the alveoli, often distended to their utmost, 

 and from them material for the formation of milk appears to be derived. 



Comparative. From ten to twelve nipples are found in rodents, insectivora 

 and carnivora ; others among these animals have only four. Pachyderms and rumi- 

 nants generally possess from two to four on the abdomen ; the carnivorous whale 

 has two at the side of the vulva. Apes, bats, herbivorous whales, elephants and 

 sloths resemble man; the half-apes have from two to four nipples. The duck-bill 

 (ornithorhynchus paradoxus) possesses tubes arranged in groups (similar to skin- 

 glands) , which open without nipples upon a hairless flat area of skin. The mar- 

 supials carry their undeveloped young in a muscular duplicature of the skin of 

 the abdomen, in which the nipples are situated. In them and in the duck-bill 

 there is a compressor muscle of the mammary gland, which promotes the evacua- 

 tion of milk. 



Development of the Breast. The first indication of the breasts consists on each 

 side in a transitory elevation passing downward on the lateral aspect of the thorax, 

 and of which subsequently there remain only punctate and nodular formations, the 

 precursors of the breasts. The further development of the latter begins in both 

 cases as early as the third month; between the fourth and fifth a number of 

 simple tube-like glandular ducts arranged radially are already present beneath 

 the hairless, excavated mammillary areola. In the new-born the ducts already 

 exhibit two or three branches, and they are provided with dilated extremities. 

 In both sexes the ducts divide in a dendritic manner until the twelfth year, though 

 without the development of actual acini. In girls who have reached puberty this 

 Branching proceeds rapidly and extensively, although also in them the gland, rich 

 in connective tissue, exhibits the formation of acini only at ,the periphery, while 

 only with the occurrence of pregnancy do characteristic acini develop also in the 

 center of the body of the gland along with relaxation of the connective tissue. 



In the climacteric period all of the acini and numerous small milk-ducts dis- 

 appear. In the adult man the mammary gland usually resembles that of the new- 

 born, having undergone involution after puberty. Supernumerary nipples on the 

 breast are of interest as representing independent openings of individual milk-ducts . 

 Supernumerary glands and nipples (hypermastia and hyperthelid) arranged in part 

 irregularly and in part regularly in rows, like the dugs of the sow, point to their 

 original multiple beginning and are worthy of note as points of resemblance 

 among animals. 



The situation of a breast in the axilla, on the back, on the acromion or on 

 the tibia is a curiosity. A slight secretion from the breast of the new-born (witches' 

 milk) is normal. On the other hand, suckling performed by a man is to be included 

 among the greatest rarities. According to Aristotle buck- goats sometimes give 

 milk (noted also by Schlossberger) , as do also calves after their dugs have been 

 frequently sucked, and goats that have not been covered, when their udders are 

 irritated by nettles. 



