CLASS MAMMALIA. MAMMALS 



465 



DOMESTIC CAT 



The domestic cat is a carnivore; its scien- 

 tific name is Felis catiis, and it belongs to 

 the same family as the lions, tigers, wild- 

 cats, and others. Often the lion is spoken of 

 as a big cat, and he is in fact one kind of 

 cat. 



External features 



The domestic cat is a 4-footed animal 

 (quadruped), which illustrates well the char- 

 acteristics of the higher mammals. It pos- 

 sesses an external covering of hair or fur, 

 two ears, and separate genital and anal open- 

 ings. The mouth is bounded by thin fleshy 

 lips. At the end of the head are two nar- 

 row nostrils. The large eyes, one on either 

 side of the head, are protected by an upper 

 and a lower eyelid bordered by fine eye- 

 lashes, and a white, hairless, third eyelid or 

 nictitating membrane, which may be drawn 

 over the eyeball from the inner angle. Above 

 and below the eyes and on the upper lip are 

 long sensitive hairs, the whiskers (vibrissae). 



The trunk may be separated into an an- 

 terior portion, the thorax, which is sup- 

 ported laterally by the ribs, and a posterior 

 portion, the abdomen. The tail is long. Be- 

 neath its base is the anus, and just in front 

 of this is the urogenital opening. In males 

 the scrotum hangs beneath the anus. There 

 are normally 4 pairs of small teats situated 

 on the ventral surface of the thorax and ab- 

 domen. At the end of the teats open the 

 ducts of the mammary or milk glands. 



The forelimbs of the cat are used, as in 

 the frog, for holding up the anterior part of 

 the body. They each possess 5 toes with 

 fleshy pads and retractile claws. The hind- 

 limbs are stouter and more powerful than 

 the forelimbs and serve as the principal 

 power in locomotion. They are provided 



Figure 337. Facing page, representatives of 18 

 different orders of mammals. These animals show 

 the many adaptations characteristic of living or- 

 ganisms. The figures are not drawn to scale. 



with only 4 toes; the one corresponding to 

 the great toe in man is absent. The cat 

 walks on its toes and is, therefore, said to 

 be digitigrade. 



Skeleton 



The skeleton of the cat (Fig. 338) con- 

 tains bones that correspond closely to those 

 in the skeleton of man. It consists princi- 

 pally of bone, but a small amount of car- 

 tilage is also present. As in the fishes, am- 

 phibians, reptiles, and birds, there are 

 cartilage bones preformed in cartilage, and 

 membrane bones arising by the transforma- 

 tion of connective tissue. A third type, called 

 sesamoid bones, occurs in the tendons of 

 some of the limb muscles, the action of 

 which they modify; for example, the knee- 

 cap, or patella. 



The axial skeleton consists, as in the 

 pigeon, of a skull, ribs, sternum, and verte- 

 bral column. The skull (Fig. 339) is formed 

 of both cartilage and membrane bones, and 

 only a small amount of cartilage. The in- 

 dividual bones are immovably united to 

 one another; their boundaries are in many 

 cases obliterated in the adult and can be 

 made out only in the embryo. 



In humans, the incomplete ossification of 

 the bones of the skull at the birth of a baby 

 indicates an adaptive mechanism for child- 

 birth. During labor the bones of the skull 

 override each other, and the infant's skull, 

 being reduced in size, accommodates itself 

 to the size of the birth canal. 



The vertebral column of the cat, as in 

 other vertebrates, supports the body and 

 protects the spinal cord. The vertebrae 

 move upon one another; are separated by 

 intervertebral disks of fibrocartilage, except 

 in the sacrum; and are connected by inter- 

 vertebral ligaments. The vertebrae of the 

 neck or cervical vertebrae are 7 in number; 

 those of the chest, the thoracic vertebrae, 

 bear movably articulated ribs; those of the 

 trunk region are called lumbar vertebrae; 

 the 3 sacral vertebrae are fused together and 

 support the pelvis; and the caudal vertebrae 



