Table 1.

Species differences in mammary anatomy [21]

Species	Number of pairs of mammae (mammary glands)				Ductal systems per mamma	References
	Cervical	Thoracic	Abdominal	Inguinal
Human		1			4–18	[22–24]
Cow				2	1	[24]
Sheep and goats				1	1	[24]
Rabbit		1	2	1	Approximately 6	[25–27] Authors’ unpublished data
Mouse	1	2	1	1	1	[24]