Development of Mammary gland of animals
An ectodermal thickening called milk line or mammary ridge extends on either side as longitudinal bands between the bases of limb buds.
The primordial band is developed in the pectoral region (Primates, elephants) inguinal region (undulates) or throughout (axilla to groin region) in carnivores and pigs.
The primordium of each gland becomes lens shaped, then globular and then lobed. From these, solid cords bud inwards into the – corium. These primary solid milk ducts branch and terminate in secretory portion of acini.
Lumen is acquired by canalisation of the solid ducts and acini.