260 ANATOMY OF THE Rx\BBIT 



The transverse artery of the neck (a. transversa colli) lies on the 

 medial side of the cervical portion. 



The thoracic portion of the serratus anterior ma}^ function as an 

 aid to breathing when the anterior limb is held firm and the muscle 

 contracts so as to raise the ribs. In this case the relations of origin and 

 insertion just described are thus reversed. 



2. Muscles arising from the axial skeleton and the pectoral girdle 

 and inserted on the humerus, for the most part at its proximal 

 extremity. 

 Note the axillary lymph glands lying in the fat of the axillary fossa. 



{a) The latissimus dorsi. Origin: Lumbodorsal fascia and 

 four posterior ribs. Insertion: Deltoid tuberosity. A long 

 flat triangular muscle, covering a considerable portion of 

 the lateral surface of the thorax; having its dorsal angle 

 covered by the thoracic portion of the trapezius. Its in- 

 sertion end passes to the medial side of the humerus. 



ih) The pectoralis primus (p. tenuis). Origin: Manubrium 

 sterni. Insertion: Deltoid tuberosity. 



A branch of the thoracoacromial artery appears between this 

 muscle and the cleidohumeralis (3, a). 



The muscle should be raised from the surface and 

 divided. 

 (c) The pectoralis secundus (p. major). Origin: Entire lateral 

 portion of the sternum. Insertion: Anterior and antero- 

 medial surfaces of the humerus, beginning below the greater 

 tubercle and extending to near the boundary between the 

 middle and distal thirds. The more anterior fibres are 

 covered by those of {h). The more posterior fibres pass 

 dorsal to the more anterior ones so that the muscle has a 

 partly twisted form and its insertion is in two layers or 

 separate slips. Some of the posterior fibres are inserted 

 highest on the humerus. By working back from the 

 clavicle, the muscle can be separated from those beneath 

 and divided. 



The more superficial layer is the thinner and is derived mainly 

 from the anterior half of the origin. It is attached along a line extend- 

 ing distad from the greater tubercle along and beyond the medial part 

 of the humeral spine. The deeper layer, derived mainly from the 



