46 ANATOMY OF THE RAT 



seters on the lower jaw. Locate its origin on the skull and 

 its insertion on the mandibles at, and near, the symphysis. 



Sternahyoideus Muscle. The two sternohyoideus muscles 

 lie on the ventral side of the neck behind the digastricus. 

 They are in contact with one another along the sagittal 

 plane of the neck. Origin, the sternum. Insertion, the 

 hyoid bone. 



The sternomastoideus and clavotrapezius muscles have 

 already been mentioned in connection with the lateral 

 view. Identify them here. 



Omohyoideiis Muscle. This muscle will be observed on 

 the ventral surface of the neck in the triangular space 

 bounded by the digastricus, sternohyoideus, and sterno- 

 mastoideus muscles. Origin, the superior margin of the 

 scapula. Insertion, the hyoid bone. 



The Pectoral Muscles are a prominent group on the ven- 

 tral side of the thorax. The pectoralis major partially con- 

 ceals the pectoralis minor. The pectoralis major consists 

 of a superficial and a deeper portion. The origin of the 

 superficial portion is the anterior half of the sternum's 

 manubrium ; it is inserted on the deltoid ridge. The deeper 

 portion originates on the manubrium of the sternum and 

 the first and second sternebrae ; the insertion is likewise on 

 the deltoid ridge. 



Pectoralis Minor Muscle. Remove the pectoralis major 

 to study this muscle. It comprises three parts. The origin 

 of the first, or most anterior, part is the second to the fifth 

 sternebrae, inclusive; insertion, on the coracoid process of 

 the scapula and the lesser tuberosity of the humerus. The 

 second, or middle, portion originates at the fifth sternebra 

 and is inserted on the deltoid ridge. The origin of the 

 third portion is the xiphoid process of the sternum; the 

 insertion is on the coracoid process of the scapula. 



Rectus Ahdomi7iis Muscle. This consists of a pair of 



