placental

But increase in size and activity, and the expense of producing each new individual, led to the adoption of placental development.

The types of dentition characteristic of the different groups of placental mammals may mostly be paralleled among the Marsupials.

The Marsupials stand in many important characters below the placental mammals.

This pouch is supported by two characteristic marsupial bones, also existing in Cloacal animals, but not in Placental animals.

Placental animals also do not possess the peculiar hooked process of the lower jaw which characterizes Marsupials.