58 The Vertebrate Organ Systems 



The Appendicular Skeleton. — The appendicular skeleton of the 

 frog consists of two girdles and the bones of the fore- and hindlimbs. 

 The anterior or pectoral girdle is C-shaped and is attached to the 

 vertebrae simply by muscles. On either side there is a broad dorsal 

 suprascapula, a narrow lateral scapula, a ventral clavicle, and a wide 

 coracoid. The coracoid joins to the midventral sternum or breast- 

 bone. Both the sternum and the suprascapula are formed chiefly of 

 cartilage. The scapula contains a depression, the glenoid fossa, into 

 which the forelimb articulates. The forelimb consists of a humerus, 

 radio-ulna, carpals, metacarpals, and the phalanges. 



The posterior or pelvic girdle is more strongly articulated to the 

 vertebral column than is the pectoral girdle. It bears the support of 

 the entire animal. The girdle itself is a V-shaped structure consisting 

 of three bones on either side : the long ilium, the short posterior ischium, 

 and the ventral pubis. The ilium articulates to the vertebral column 

 by means of exceptionally long transverse processes on the ninth vertebra. 

 At the junction of these three bones of the girdle is a socket, the 

 acetabulum. The head of the femur of the hindlimb articulates with 

 this socket. The bones of the hindlimb consist of the long heavy femur, 

 the tibio-fibida, the tarsals, metatarsals, and the phalanges. 



THE MUSCULAR SYSTEM 



Like all other animals that move about constantly in search of 

 food or in order to escape enemies, the frog has a well-developed mus- 

 cular system. 



From both a histological and functional point of view, three sep- 

 arate types of muscles are recognizable. The first of these, cardiac, 

 are found only in the heart. These muscle fibers are branched. The 

 second important type are the smooth or nonstriated muscles which are 

 found throughout the visceral organs. These muscles are not under 

 conscious control, but are very important for the bringing about of 

 many movements such as the passage of food down the digestive 

 tract. The third class of muscles, the skeletal or striated muscles, 

 are the large muscles which are responsible for all conscious movements. 

 In general, it can be stated that muscles of some type are found wher- 

 ever movements are needed. 



The individual muscle fibers are about 4 to 5 cm. long and 

 are bound together by means of connective tissue into the muscles. 

 Generally the skeletal muscles are attached by either one or both ends 



