250x250px Mammary glands are arranged in breasts of the primates to produce milk for feeding offspring. They are enlarged and modified sweat glands. In the embryological development, mammary glands firstly appear after six weeks of pregnancy in the form of ectodermal ridges. The ectodermal ridge grows thicker and compresses to form mesoderm. As the proliferation persists, mesodermal layer continues to form clusters. The clusters grow and become lobules. At the same time, the clusters also form a pit, which protrudes to generate the nipples. Impairment in some of these processes may cause aplasia of the breast tissue, which may result in<unk> . For example, in normal condition, mammary ridge (milk line) would extend from the bilateral axillary tail to the inguinal region. If this extension does not occur in normal way, the breast would not develop successfully.<unk>  may also be caused by the inability of producing parathyroid hormone related protein. The absence of this protein will disrupt the normal development of mammary gland. Therefore, when<unk>  patients receive medical ultrasound examination, asymmetry or disproportioned mammary tissue may be found.
Amastia
Hamartia 
Macrodontia 
Macrotia
Acrania
Spotted lunulae
Cystic eyeball
Auricular hypertrichosis