In what state of development is a newly born kitten? With what does the cat _nourish its young_? Name ten animals of various kinds whose young are similarly nourished. What is this class of animals called? Why does a cat bend its back when it is frightened or angry? Does _a cat or a dog_ eat a greater variety of food? Which refuses to eat an animal found dead? Will either bury food for future use? Which is sometimes troublesome by digging holes in the garden? Explain this instinct. Which lived a solitary life when wild? Which had a definite haunt, or home? Why are dogs more sociable than cats? A dog is more devoted to his master. Why? A cat is more devoted to its home, and will return if carried away. Why? Why does a dog turn around before lying down? (Consider its original environment.) [Illustration: FIG. 337.--SKELETON OF CAT.] =The Skeleton= (Fig. 337).--Compare the _spinal column_ of a cat in form and flexibility with the spinal column of a fish, a snake, and a bird. The _skull_ is joined to the spinal column by two knobs (or _condyls_), which fit into sockets in the first vertebra. Compare the jaws with those of a bird and a reptile. There is a prominent ridge in the temple to which the powerful chewing muscles are attached. There is also a ridge at the back of the head where the muscles which support the head are attached (Fig. 348). [Illustration: FIG. 338.--CLAW OF CAT (1) retracted by ligament, and (2) drawn down by muscle attached to lower tendon.] Count the _ribs_. Are there more or fewer than in man? The breastbone is in a number of parts, joined, like the vertebræ, by cartilages. Compare it with a bird’s sternum; why the difference? The shoulder girdle, by which the front legs are attached to the trunk, is hardly to be called a girdle, as the collar bones (clavicles) are rudimentary. (They often escape notice during dissection, being hidden by muscles.) The shoulder blades, the other bones of this girdle, are large, but relatively not so broad toward the dorsal edge as human shoulder blades. The clavicles are tiny because they are useless. Why does the cat not need as movable a shoulder as a man? The pelvic, or hip girdle, to which the hind legs are attached, is a rigid girdle, completed above by the spinal column, to which it is immovably joined. Thus the powerful hind legs are joined to the most rigid portion of the trunk. =Mammals.=--The cat belongs to the _class Mammalia_ or mammals. The characteristics of the class are that the young are not hatched from eggs, but _are born alive, and nourished with milk_ (hence have lips), and the _skin is covered with hair_. The milk glands are situated ventrally. The position of the class in the animal kingdom was shown when the cow was classified (p. 9). Their care for the young, their intelligence, and their ability to survive when in competition with other animals, causes the mammals to be considered the highest class in the animal kingdom.