58 A MANUAL OF ZOOLOGY 



scapula. What is its origin? Ventral to ttie latissimus 

 dorsi and posterior to the scapula find a muscle, the op- 

 ponens levator clavicula, similar in shape to the former. 

 Its origin is on the 'outer end of the third or fourth trans- 

 verse process, and its insertion is on the posterior border 

 of the scapula. Immediately antero-external to the sterno- 

 radialis find a narrow muscle, episterno-deltoid. Its origin 

 is on the outer edge of the episternum and its insertion 

 is on the posterior surface of the deltoid ridge near the 

 distal end of the humerus. Note the relation of the muscle 

 to the sterno-radialis. The deltoid is located dorsal to the 

 episterno-deltoid and ventral to the infraspinatus. Its orig- 

 in is on the anterior edge of the scapula, and its insertion 

 is on the deltoid ridge, almost its entire length. Three 

 muscles comprise the group known as the triceps brachia. 

 They are all inserted in one tendon on the olecranon pro- 

 cess of tne radio-ulna. Trace each division to its origin. 

 Two thick muscles invest the insertion of ^e deltoid. 

 They may be called the pronator, and the supinator. 

 Trace out both the origin and the insertion of these mus- 

 cles, and decide why these names are given to them. The 

 ejctensor muscles are located on the externo-ventral sur- 

 face of the radio-ulna. Two divisions of these muscles 

 may be made, an anterior and a posterior. On the anter- 

 ior dorsal surface of the radio-ulna or ante-brachium are 

 found the flexor muscles. Three divisions of these mus- 

 cles may be made. From their position and direction 

 what would be the result of their actions? 



Muscles of the Hind Limb — In the act of swimming 

 or jumping the frog extends his hind legs backward until 

 they occupy a position parallel to the longitudinal axis of 

 the body. Specimens that have been preser^ved in alcohol 

 or formalin are not usually found thus, but for purposes 

 of description this longitudinal position will be assumed. 

 The surface along which lie the extensor muscles of the 

 legs, the patellar surface of the knee, and the upper surface 

 of the foot, will be called the outer or external surface. 

 The surface opposite along the bend of the knee and cov- 

 ered by the flexor muscles, will be called the inper or 

 internal surface of the leg. Concerning the surfaces 



