76 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



they begin to caniculize (7th to 9th months). At or about birth 

 the pit or depression, from which the lobular buds originated, is 

 raised, evaginated and forms the surface of the nipple (Fig. 5 7 D). 



B -£j4vy^r c - 



mg$m * mp$m 



Fia. 57. — Showing the various stages in tho development of the Mamma. 



A. During the 2nd month. B. At the commencement of the 3rd month. C. At the 



5th month. D. At birth. 



A=Epiblast. b = Subcutaneous tissue (mesoblast). c = Pectoralis major. 



Thus the ducts come to open on the apex of the nipple. An 

 ampulla is developed in each duct within the base of the nipple. 

 Stage 3 represents the marsupial — the lowest mammalian form of 

 mamma. 



Stages after Birth. — Stage 5 occurs at puberty ; the latent 

 infantile lobular buds again undergo a rapid growth and give rise 

 to the minor lobules and acini. Stage 6 occurs towards the end 

 of pregnancy and consists of a renewed production of glandular 

 tissue. Stage 7 sets in with the menopause and is characterized 

 by an atrophy of the glandular tissue formed in the later stages of 

 development. 



In the process of subdivision, minor buds of adjacent lobes 

 frequently unite together. Hence it is found difficult, during 

 dissection, to separate the gland into its primary lobes. In any 



