[Truncated abstract] In women, as in other mammals, the ability to successfully lactate depends on both complete functional development of the mammary gland and the stimulation of the milk ejection reflex to enable the suckling young to remove stored milk. Prior to my studies, Sir Astley Cooper’s carried out the most comprehensive investigation of the gross anatomy of the lactating human breast in 1840. I have used ultrasound to image the anatomy of the breasts of fully breastfeeding women (1-6 months, n=22) with particular emphasis on the distribution of the main milk ducts, glandular and adipose tissue. Scanning of the milk duct system demonstrated that the anatomy in the region of the areola and nipple is different to that depicted in standard anatomical textbooks. The main milk ducts were small (diameter, left: 1.9 ± 0.6 mm; right: 2.1 ± 0.7 mm), superficial (depth, left: 4.50 ± 1.98 mm; right: 4.74 ± 1.59 mm) and branched close to the nipple (within 8.20 ± 6.27 mm, left; 7.00 ± 3.98 mm, right) (mean ± SD). The lactiferous sinuses (described in current textbooks) were not observed and the number of main ducts detected at the base of the nipple was less than the quoted 15-20 (9.4, range 4-18). Quantitative descriptions of the morphology of either the lactating or, indeed, the non-lactating breasts have not been attempted using ultrasound. I developed a systematic approach to ultrasound imaging of the breast that provided a semi-quantitative description of the distribution of glandular and adipose tissues within the lactating breast. Approximately two thirds of the breast was comprised of glandular tissue. Intraglandular fat was identified as hypoechoic transects within the hyperechoic glandular tissue. Over 65% of the glandular tissue together with 50% of the intraglandular fat and 25% of the subcutaneous fat was located within a 30 mm radius of the base of the nipple. The absence of lactiferous sinuses and the arrangement of tissue within a 30 mm radius of the nipple suggested that the current conceptualisation of sucking dynamics of the infant requires revision. Successful milk removal depends on the stimulation of the milk ejection reflex and currently subjective assessments of milk ejection such as the mother’s sensations and an alteration in the infants sucking and swallowing are used clinically to confirm milk ejection whereas in research two stressful invasive procedures; changes blood oxytocin and intra-ductal pressure have been used. I have developed a non-invasive ultrasound technique to detect milk ejection in women