2o8 Anatomy of the Rabbit. 



(d) The pectoralis tertius (p. minor) . Origin consisting of two 

 portions : 



First portioji : Anterior portion of sternum to attachment of 



fourth rib. 



Second portion: Manubrium stemi arid costal cartilage of 



first rib. 



Insertions The superficial fibres of the first portion are 



attached to the clavicle. The remaining fibres, combined 



with those of the second portion and those of the pecto- 



scapularis, pass to the dorsal side of the clavicle and over the 



shoulder to be inserted on the scapular spine. The muscle 



forms a broad fleshy mass covering the anterodorsal portion 



of the shoulder. 



(e) The pectoralis quartus. Origin: The sternum, from the 

 attachment of the fourth to seventh costal' cartilages. In- 

 sertion: Anterior surface of the head of the humerus, passing 

 thence to its medial side. The muscle overlaps the more 

 posterior fibres of the first portion of (d). 



(f) The pectoscapularis. Origin: The manubrium stemi at 

 the point of attachment of the first costal cartilage. In- 

 sertion as indicated above. A slender muscle concealed 

 by the p. tertius, which should be divided. 



Bloodvessels and Nerves of the Axillary Fossa. 



After division of the pectorals and the clavicle, the bloodvessels 

 and nerves of the axillary fossa will be fully exposed. 



*The axillary artery (a. axillaris), the continuation of the 

 subclavian, crosses from the first rib to the medial surface 

 of the humerus, where it is replaced by the brachial artery. 

 Its branches are : 



(a) The transverse scapular (suprascapular) artery (a. 

 transversa scapulae); it arises from the anterior wall, and 

 taking a position dorsal to the clavicle accompanies the 

 p. tertius and pectoscapularis to the front of the shoulder, 

 where, under cover of these muscles, it passes into the supra- 

 spinatus muscle. 



