Mammals are the most successful and dominant animals today. They thrive very well in most of the environment of the world. Unique mammalian characteristics are: (a) Body covered with hair.(b) Presence of sebaceous and sweat glands in the skin.(c) Presence of mammary glands in females.(d) The heart is four chambered.(e) The red blood corpuscles (erythrocytes) are biconcave and enucleated.(f) Corpus callosum unites two cerebral hemispheres.(g) Testes are extra-abdominal in scrotal sacs.(h) Presence of penis for copulation in males.(i) Mostly viviparous and embryo attached to the uterine wall by the placenta.