The body is wrapped in a thick layer of fat, known as blubber. This provides thermal insulation and gives cetaceans their smooth, streamlined body shape. In larger species, it can reach a thickness up to 50 cm. Hind legs are not present in cetaceans, nor are any other external body attachments such as a pinna.

The reproductive organs of both sexes and the mammary glands of females are sunken into the body. The male