Mammalia: Skin, Muscles, Skeleton 



579 



CUT LIMB BUD 



POSITION OF DEFINITIVE GLAND 



GLAND ANLAGE 



EPIDERMIS -...t:. 

 SMOOTH MUSCLE.SLi 



COPJUM "-Si** 



13.5MM. HUMAN EMBRYO. 



B MUSCLE 



FlG. 447. A figure illustrating the development of the mammary gland in man. 

 A 13. 5 mm. embryo (left) shows the "milk-line," a ridge which extends from the 

 axillary region to the groin. The definitive gland develops only from the anterior 

 portion of this line. (Redrawn from \rey, after Kollmann.) 



(A, B, C) Sections of the definitive mammary gland in successive stages of 

 development. (A) From a two-month embryo. (B) From a four-month embryo. 

 (C) From a seven-month embryo. The mammary gland is a compound tubular 

 gland. (Redrawn from Arey, after Tourneux.) (Courtesy, Neal and Rand: "Chor- 

 date Anatomy," Philadelphia. The Blakiston Company.) 



Fig. 448. Scheme of different kinds of nipples. Single line indicates ordinary 

 integument; double line, that of primary mammary pocket. (A) Primitive condi- 

 tion, found in Echidna. (B) Human nipple. (C) Didelphys at lactation. (D) Didel- 

 phys before lactation. (E) Embryonic conditions in cow. (F) Adult conditions in 

 cow. (B) and (C) are true nipples, (F) a pseudonipple (teat). (After Weber. Cour- 

 tesy, Kingsley: "Comparative Anatomy of Vertebrates," Philadelphia, The 

 Blakiston Company.) 



