256 THE BIOLOGY OF THE FROG chap. 



The transversus is a broad muscle lying beneath the ex- 

 ternal oblique and forming the innermost muscular layer of 

 the body wall. Its fibers run for the most part transversely. 

 Anteriorly some of its fibers are inserted into the esophagus 

 and closely overlie the pericardium ; other fibers attach to 

 the coracoid and xiphisternum ; the posterior portion of the 

 muscle is inserted into a flat tendon which extends dorsally 

 to the rectus abdominis to the mid-ventral line. All of these 

 muscles have the general effect of contracting the body 

 cavity. 



The cutaneous pectoris, a paired muscle lying on the ven- 

 tral side of the anterior part of the body. Posteriorly it is 

 attached to the body wall, and it is inserted anteriorly into 

 the skin between the fore legs. 



The pectoralis major, a large muscle on either side of the 

 anterior part of the body. It is composed of three parts, an 

 abdominal portion arising from the sides of the anterior half 

 of the rectus abdominis, a middle portion arising from the 

 sternum and xiphisternum, and an anterior portion arising 

 from the coracoid and epicoracoids. All three parts are in- 

 serted near together on the ventral crest of the humerus. 



The submaxillary muscle extends transversely across the 

 floor of the buccal cavity, between the two rami of the lower 

 jaw. It raises the floor of the buccal cavity in respiration. 



The submentalis is a small muscle lying in the anterior 

 angle of the lower jaw. Its fibers run transversely, and by 

 their contraction raise the tip of the jaw and thereby bring 

 about the closure of the nares in respiration. 



The subhyoid, a small muscle arising from the anterior 

 corner of the hyoid near the skull and joining ventrally the 

 posterior margin of the submaxillary. It raises the hyoid. 



The following muscles are attached to the hyoid and take 

 part in the movements of respiration : The geniohyoid, 



