346 



COLLEGE ZOOLOGY 



cartilage. The suprascapulae lie above the 

 vertebral column, and the rest of the girdle 

 passes downward on either side and unites 

 with the sternum in the ventral middle line. 

 The principal parts of the pectoral girdle 

 are: the suprascapulae, scapulae, clavicles, 

 coracoids, and epicoracoids; of the sternum: 

 the episternum, omosternum, mesosternum, 

 and xiphisternum. The end of the long bone 

 of the forelimb ( humerus ) lies in a concav- 

 ity in the scapula and coracoid called the 

 glenoid fossa. 



The pelvic girdle supports the hindlimbs. 

 It consists of two sets of three parts each: 

 the ilium, the ischium, and the pubis. The 

 pubis is cartilaginous. The anterior end of 

 each ilium is attached to one of the trans- 

 verse processes of the ninth vertebra. Where 

 the parts of each half of the pelvic girdle 

 unite, there is a concavity called the 

 acetabulum, in which the head of the long 

 leg bone (femur) lies. 



The forelimb consists of a humerus which 

 articulates with the glenoid fossa of the 



pectoral girdle at its proximal end and with 

 the radioulna at its distal end. The bone of 

 the forearm (radioulna) consists of the 

 radius and ulna fused. The wrist contains 6 

 bones arranged in two rows, each consisting 

 of three small bones (carpals). The palm of 

 the hand is supported by 4 proximal meta- 

 carpal bones, followed by digits 2 and 3 

 which consist of 2 phalanges each, and by 

 digits 4 and 5 which consist of 3 phalanges 

 each, and the rudimentary thumb is repre- 

 sented by the first metacarpal. 



The hindlimb consists of (1) a femur 

 (thighbone), (2) a tibiofibula (the tibia 

 and fibula fused) or lower leg bone, (3) 

 four tarsal bones, the astragalus, the calcan- 

 eum, and 2 smaller bones, (4) the 5 

 metatarsals of the sole of the foot, (5) the 

 phalanges of the digits, and (6) the prehal- 

 lux ( calcar ) of the accessory digit. The two 

 pairs of limbs differ in size but have similar 

 component bones. This is easily seen in the 

 accompanying table. 



FORELIMB (arm) 



NO. OF BONES 



HINDLIMB (leg) 



NO. OF BONES 



The skeletons of animals in general and 

 of man in particular are described in Chap- 

 ter 31. 



Muscular system, motion, 

 and locomotion 



The main function of the muscular sys- 

 tem is to cause movement by contraction. 

 Muscles (Figs. 230 and 231) are of three 

 principal types— smooth, cardiac, and stri- 

 ated, which is of a skeletal type; these dif- 

 fer in their microscopic structure and func- 

 tion. Smooth muscle is involuntary muscle. 

 Cardiac muscle is "involuntary" striated 

 muscle that occurs in the vertebrate heart 



only. Striated muscle of the skeletal type- 

 that is, the muscles of the external muscular 

 system — is voluntary muscle. 



Muscle fibers may be 4 or 5 cm. long and, 

 when bound together by connective tissue, 

 form the larger bundles known as muscle. 

 Skeletal muscles are usually attached by one 

 or both ends to bones either directly or by 

 means of a tendon, which is an inelastic 

 band of connective tissue (Fig. 43). The 

 two ends of a muscle are designated by dif- 

 ferent terms: the origin is the end attached 

 to a relatively immovable part; the insertion 

 is the movable end. Usually the origin is near 

 the spinal axis of the body, while the inser- 

 tion is peripheral. A muscle which bends one 



