208 ANATOMY OF THE RABBIT. 
(d) The pectoralis tertius (p. minor). Origin consisting of two 
portions: 
First portion: Anterior portion of sternum to attachment of 
fourth rib. 
Second portion: Manubrium sterni and costal cartilage of 
first rib. 
Insertion: 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 sterni 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. 
