Taxonomic List and Nomenclature Used

The class Mammalia is defined by having mammary glands which produce milk; hair present, although confined to early development; mandibular ramus of the lower jaw made up of a single bone; lower jaw articulating directly with the skull; two exoccipital condyles that articulate with the atlas; a diaphragm dividing the pulmonary area; red blood corpuscles not nucleated; “warm blood”; complete double circulation; heart four-chambered; presence of amnion and allantois. With two Infraclass Metatheria: placenta absent or incomplete; epipubic bones present or rudiments in both sexes; skull with a small braincase and a large preorbital region; nasals expanded posteriorly; jugal bone contributing to the glenoid fossa; tympanic bone small, annular or tubular, rarely fused with other skull bones; auditory bullae, if present, formed entirely or principally from the alisphenoid bone; young born in a notably undeveloped condition and it develops while firmly attached to mammae in an abdominal pouch; brain lacking corpus callosum. Infraclass Eutheria: placentalia differs from other mammals in that the fetus is carried in the mother’s uterus until a relatively late development stage; there are not epipubic bones; malleolus is at the bottom of the fibula; and rearmost bones of the foot fit into a socket formed by the ends of the tibia and fibula, forming a complete mortise and tenon upper ankle joint.