• Linear thickening of surface ectoderm (milk line) appears on ventral body
• Extends from axilla to medial inguinal region
• Line disappears except in pectoral region

• 15 to 20 solid ectodermal buds arise in remaining milk line
• Buds form solid cords
• Which grow in underlying mesenchyme
• Cord grows and branches in fetal life
• Canalized before birth to form: Lactiferous sinus, Lactiferous duct, Secretory alveoli
• Open in depressed area, which elevates after birth – to form the nipple

At puberty:

• Males: have ducts without alveoli
• Females: Ovarian hormone increases branching of lactiferous duct, and increases fat between lobules. Therefore the mammary gland enlarges.

Congenital anomalies:

1. Amastia – absence of one or two mammary glands
2. Athelia – absence of one or two nipples
3. Macromastia – large breasts
4. Micromastia – small breasts
5. Polythelia – accessory nipples
6. Polymastia – accessory breast
7. Gynaecomastia – male developing female breasts
8. Klinefelter syndrome – XXY in males, therefore have enlarged breasts, wide hips and penis does not grow