THE MUSCULAR SYSTEM 43 



clavicle. Insertion, the lateral part of the crest that runs 

 dorsally from the external auditory meatus. 



Sternomastoideus Muscle. This muscle is anterior, and 

 parallel to, the clavotrapezius. Origin, the anterior end 

 of the manubrium. Insertion, by a tendon to the mastoid 

 bone. 



Spinotrapeziiis Mitscle. Origin, (1) the spines of the 

 fourth to the thirteenth thoracic vertebrae; (2) from the 

 lumbodorsal fascia from the level of the thirteenth thoracic 

 to the third lumbar vertebra. Insertion, the scapular 

 spine. It draws the scapula dorsocaudad. 



Latissimus Dorsi Muscle. This is a triangular muscle 

 attached at one of its angles to the medial side of the 

 humerus. Origin : the spines of the thoracic vertebrae from 

 the eighth to the twelfth, inclusive, and the lumbodorsal 

 fascia to the level of the third lumbar vertebra. Insertion, 

 by a strong tendon to the medial surface of the humerus. 

 It is also strongly united to the muscles lateral to it in 

 the axillary region. The fibers converge to the tendon of 

 insertion. It pulls the arm caudodorsad. 



Acromiodeltoideus Muscle. Origin, the acromion and 

 metacromion processes of the scalpa, and the ventral border 

 of the clavicle. Insertion, the deltoid process of the hu- 

 merus. The acromiodeltoideus is bipinnate ; the fibers from 

 the clavicle form an acute angle with those from the acro- 

 mion and metacromion processes where these two groups of 

 fibers join a connective tissue septum ventral to the hu- 

 merus. This septum forms the connection of the muscle 

 with the deltoid process. 



Spinodeltoideus Muscle. Origin,^ the infraspinous fascia 

 and anterior two-thirds of the spine of the scapula. Inser- 

 tion : it is united ventrally by an aponeurosis with the free 

 edge of the deltoid tuberosity of the humerus. It flexes the 

 humerus and rotates it outward. 



