644 TEXTBOOK OF ZOOLOGY 



extend in an arch, ventrally. The nine anterior ones are called 

 true rihs because they articulate dorsally with the thoracic vertebrae 

 and ventrally with the sternum, or breastbone. The other four are 

 termed false ribs, three pairs of which articulate with other ribs, 

 while the fourth has no ventral articulation and is called a floating 

 rih. The sternum is divided into eight pieces, called sternehrae, which 

 lie in a row in the median line of the ventral side of the thorax. The 

 anterior sternehra is called the manubrium and the posterior one is 

 called the xiphoid or ensiform process. 



The two girdles and pairs of limbs are quite well developed. The 

 forelimb and pectoral girdle are composed of a scapula, poorly de- 

 veloped clavicle, humerus, uhia, radius, seven carpals, five meta- 

 carpals, and fourteen phalanges. The hindlimb and pelvic girdle are 

 composed of the iyinominate bone (ilium, ischium, pubis), femur, 

 patella, tibia, fibula, seven tarsals, five metatarsals, and twelve 

 phalanges. 



Muscular System 



The study of the muscular system is known as myology. All mus- 

 cles moving the bones are voluntary; i.e., they are under control of 

 the will. There are over five hundred voluntary muscles in the cat, 

 each of which is attached by one or both ends to the periosteum of 

 the bone, usually by tendons. The point of attachment on the fixed 

 bone, which is not moved by the contraction, is the origin. The end 

 of the muscle attached to the bone which is moved is known as the 

 insertion. According to function the skeletal muscles are grouped as 

 flexors, extensors, adductors, abductors, rotators, elevators, depressors, 

 and sphincters. A flexor muscle is one which bends the part on itself. 

 An extensor is one which by its action tends to extend or straighten 

 the part. An adductor muscle is one attached to a long bone in such 

 a way as to move it toward the ventral midline of the body. An 

 abductor opposes the action of the adductor. The caudofemoralis is 

 an abductor of the thigh and flexor of the shank. The gracilis on the 

 medial surface of the thigh is an adductor of the thigh. A rotator 

 muscle is one which causes a part to rotate on its own axis. An elevator 

 raises or elevates a part, as the splenius of the neck may elevate the 

 head. A depressor is the antagonist of an elevator. A sphincter 

 muscle is one encircling an aperture which it closes by contraction. 

 The orbicularis oris in the lips around the mouth is an example. A 



