1. 32.1 Introduction to the Mammals

2. Mammary Gland Gland in mammals that produces milk to nourish the young.

3. Subcutaneous Fat Layer of fat cells beneath the skin that helps conserve body heat.

4. Rumen Stomach chamber in cows and related animals in which newly swallowed plant food is stored and processed.

5. Diaphragm Large, flat muscle at the bottom of the chest cavity that helps with breathing.

6. Cerebral Cortex Outer layer of the cerebrum of a mammal’s brain; center of think and other complex behaviors.

7. Key Concept In addition to having hair and the ability to nourish their young with milk, all mammals breathe air, have four-chambered hearts, and are endotherms that generate their body heat internally.

8. Key Concept The first true mammals appeared during the late Triassic Period, about 220 million year ago.

9. Key Concept The ability of mammals to regulate their body heat from within is an example of homeostasis.

10. Key Concept As mammals evolve, the form and function of their jaws and teeth became adapted to eat foods other than insects.

11. Key Concept The kidneys of mammals help maintain homeostasis by filtering urea from the blood, as well as by excreting excess water or retaining needed water.