How many mammary glands do mice have? - briefly
Mice possess ten mammary glands, arranged as five bilateral pairs along the ventral surface. This number is consistent across common laboratory strains.
How many mammary glands do mice have? - in detail
Mice possess a limited set of mammary glands compared with larger mammals. Adult laboratory mice typically have five pairs of functional glands, totaling ten. The pairs are numbered from the cranial (front) to caudal (rear) positions:
- Pair 1: Located near the axilla, close to the forelimb.
- Pair 2: Situated in the thoracic region.
- Pair 3: Found in the abdominal area, often the largest.
- Pair 4: Positioned near the inguinal region.
- Pair 5: Located in the perineal region, adjacent to the genitalia.
Each gland consists of a ductal system, an alveolar network for milk secretion, and a surrounding stroma. Development begins embryonically; the mammary buds appear around day 10.5 of gestation and differentiate into mature glands by birth. In males, the same anatomical sites are present, but the glands remain rudimentary and non‑functional due to androgen‑mediated suppression.
Strain differences can modify the count. Certain wild‑type or outbred strains may exhibit an additional sixth pair in the cervical region, though this is rare. Mutations affecting the Wnt or FGF signaling pathways can also lead to supernumerary or absent glands.
Physiological activation occurs during pregnancy and lactation. Hormonal cues—primarily estrogen, progesterone, and prolactin—induce alveolar proliferation, secretory differentiation, and milk production. After weaning, involution reduces glandular tissue, leaving a residual ductal network.
In summary, the standard laboratory mouse carries ten functional mammary glands organized in five bilateral pairs, with occasional strain‑specific variations and clear sexual dimorphism in development and function.