76 GENERAL ZOOLOGY 



the mouth, where it turns back and continues to the tip of the 

 tongue. 



The following muscles are found on the ventral and lateral 

 walls of the trunk. The deltoideus, arising from the clavicle, 

 precoracoid, omosternum, and scapula, is inserted on the deltoid 

 ridge of the humerus. Its contraction draws the limb forward. 

 The sternoradialis arises in the mid-line from the omosternum and 

 epicoracoid, passes outward, piercing the distal portion of the 

 deltoid, and is inserted on the radioulna. It corresponds to the 

 human biceps muscle and its contraction flexes the forearm. 

 The recti abdominis muscles of each side meet in mid-line in a tendi- 

 nous union, called the linea alba. Each rectus muscle is also 

 traversed by four or five transverse inscriptiones tendineae, which 

 are tendinous insertions in the muscle. As each rectus muscle 

 passes forward from its origin in the pubis, it widens and at the 

 second inscriptio tendinea from the rear divides into two parts : a 

 median portion continuing straight forward to the xiphisternum 

 and beyond; a lateral portion branching off to the shoulder to 

 form the abdominal component of the pectoralis muscle. The 

 continuation of the median portion beyond the xiphisternum 

 forms the sternohyoideus, which is inserted on the hyoid bone. 

 The pectoralis muscle consists of three parts; of which the 

 sternalis anterior, in front, and the sternalis posterior, just behind, 

 both have a broad origin from the epicoracoids, sternum, and 

 xiphisternum, while the abdominalis portion arises principally in 

 the rectus abdominis. All three portions of the pectoralis 

 muscle are inserted in the humerus. If the pectoral muscle is 

 removed (right side of Fig. 47), the coracohumeralis is exposed. 

 This is a narrow muscle having its origin in the coracoid near the 

 sternum and its insertion on the middle of the humerus. Pos- 

 terior to the coracohumeralis a small portion may be seen of the 

 obliquus internus (or transversus) muscle, which forms the inner 

 layer of the abdominal wall. Its origin is principally in the 

 ilium and transverse processes of the last six vertebrae. Its 

 points of insertion are various, such as the xiphisternum, coracoid, 

 esophagus, pericardium, and the linea alba. The obliquus 

 externus, whose fibers run almost at right angles to those of the 

 obliquus internus, forms the outer wall of the abdominal cavity 

 except ventrally where it is overlaid by the recti abdominalis 

 and pectoral muscles. 



