78 HUMAN EMBRYOLOGY AND MORPHOLOGY. 



through the septal or interstitial vessels with the superficial 

 mammary and deep (retro-mammary) lymphatics (Fig. 58). The 

 superficial communicate with the subcutaneous ; the deep with those 

 in the pectoral sheath and thus it will be seen that mammary cancer 

 may spread to the skin or pectoralis major. The deep and super- 

 ficial join in the circum-mammary lymphatics, and from these pass 

 efferent vessels to the pectoral and central glands of the axilla. 

 The lymph passes from these to the deep axillary and inferior 

 deep cervical glands — all of which are involved in late stages 

 of cancer of the breast. Other efferent vessels pass from the 

 circum-mammary to the anterior intercostal glands of the upper 

 four spaces ; one or two vessels may go to the cephalic gland. 



Peripheral Remnants. — Isolated or semi-isolated small masses 

 of glandular substance are found situated in the circum-mammary 

 tissue, beyond the body of the gland. Some may pierce the 

 sheath of the pectoralis major and become a source of recurrent 

 cancer. The presence of glandular remnants is explained by the 

 fact that, when the primary budding takes place, the subdermal 

 mesoblast is shallow and of small extent ; in the subsequent 

 growth of the thorax, the tissue in which the mamma is developed, 

 is widely spread out. 



The position of the Mammary Gland is as a rule wrongly described. 

 Quite a third lies on the serratus magnus and beyond the anterior 

 border of the axilla. The axillary lobe reaches upwards in the 

 axilla to the upper border of the third rib, where it is in contact 

 with the central set of lymphatic glands (Stiles). 



Fat begins to be deposited in the subcutaneous tissue during 

 the 5 th month of foetal life. It forms a large element of the 

 mammary gland after puberty. The subcutaneous tissue, out of 

 which the capsule of the gland is formed, normally contains much 

 fat. After lactation, when the glandular tissue atrophies to a 

 considerable extent, a growth of fat replaces it. If no fat is 

 deposited or if it be absorbed, then the breast loses its plump form 

 and hangs on the chest. 



The mammary nerves (secretory) come from the 3rd, 4th, and 

 5th intercostals ; the nipple is supplied from the same nerves. 

 The nipple contains non-striated muscle and is covered with 

 touch papillae and surrounded by modified sweat and sebaceous 

 glands. 



