353 ANATOMICAL TECBNOLOQT. 



its dorsal surface. It extends only 2-3 mm. before dividing into 

 two trunks. One extends caudad on the ental wall of the thorax, 

 supplies the 1st and 2d intercostal spaces, and then passes between 

 the 1st and 2d ribs to be distributed to the deep muscles of the back. 

 It may be followed by tearing away the muscles with the tracer. 

 Its final distribution can best be followed after the removal of the 

 scapula. Tlie other branch passes cephalad nearly parallel with 

 the A. vertebralis, and reaches the dorsal side of the great nerve 

 trunks of the brachial plexus (Pig. 107). It is distributed to the 

 M. serratus magnus (§ 664). After the section of the brachial ves- 

 sels and nerves and the lateriduction of the scapula, it may be very 

 easily traced. 



§ 937. Axis thyroideus (Fig. 105, A. spscp.) — Just laterad of 

 the 1st rib, this trunk takes its origin. It passes laterad along the 

 ental surface of the clavo-trapezius muscle, sending two or three 

 branches cephalad, the most important one being to tiie longus colli 

 muscle. The part extending laterad is called the A. suprascapu- 

 laris. The A. suprascapularis supplies the clavicular end of the 

 M. clavo-trapezius and the lateral surface of the supraspinatus. 

 Its principal branch, however, accompanies the suprascapular nerve 

 between the supraspinatus and subscapiilaris muscles and enters 

 the suprascapular fossa about opposite the base of the acromion. 

 In the supraspinous fossa it divides into two branches, one being 

 distributed to the muscles in the supraspinous fossa, whUe the 

 other passes through the incisura magna (Fig. 45) and is distributed 

 to the structures in the infraspinous fossa (Fig. 43). The scalpel 

 as well as the tracer should be used in tracing this vessel. 



§ 938. A. axillaris (Fig. 105, A. axl.).— This is the continuation 

 of the A. subclama laterad of the 1st rib. It is very intimately 

 associated with the axillary veins and nerves. 



§ 939. A. thoracica anterior (Fig. 102 and 105, A. thr. ant.).— 

 This is the first branch furnished by the A. axillaris. It arises from 

 the ventral surface of the axillary and passes with the nerve of the 

 same name (Fig. 105) ventrad to the pectoral muscles. If the pecto- 

 rals were divided at the proper level, this artery would remain with 

 the arm. 



§ 940. A. thoracica longa (Fig. 102 and 105, A. thr. longa).— 

 It arises at about the same level as the preceding (§ 939) and passes 

 nearly caudad, sending several small branches to the pectorals, but 



