THE ARTERIES. 293 



(A. intercostalis suprema), passes caudad and, dividing, sup- 

 plies the first and second intercostal spaces, and then passes to 

 the deep muscles of the back. The other branch divides almost 

 immediately into two. One of these, A. transversa colli, 

 passes laterad in front of the first rib and enters the serratus 

 anterior muscle. In this it passes dorsad, giving off branches 

 to this muscle and to the levator scapulae, till it reaches 

 M. rhomboideus, which it likewise supplies. The other branch 

 (A. cervicalis profunda), which seems to form a continuation 

 of the main artery, passes directly dorsad and leaves the 

 thoracic cavity between the heads of the first and second ribs. 

 Here it passes into the deep muscles of the neck ; it can be 

 traced in the substance of the complexus muscle as far forward 

 as the atlas. 



d. Truncus thyreocervicalis (Fig. 118,7'). ^ e thyro- 

 cervical axis (or thyroid axis) arises from the subclavian 

 beneath the first rib, a short distance distad of the origin of the 

 costocervical axis. It passes laterocraniad and dorsad, lying 

 on the mediocranial side of the brachial plexus. A short dis- 

 tance from its origin it gives off a branch, varying much in 

 size, the cervicalis ascendens (Fig. 119, </), which passes 

 craniad on the ventral side of the neck, supplying the sterno- 

 mastoid, sternohyoid, the cervical portion of the scalenus, and 

 sometimes other muscles of the neck region. Other branches 

 pass from the thyroid axis to the inner surface of the clavo- 

 trapezius (Fig. 122, a) and to the ventral end of the 

 pectoral muscles. At the level of the cranial border of the 

 scapula the artery takes the name A. transversa scapulae, or 

 suprascapularis. This divides into three main branches. The 

 first branch, sometimes large, sometimes small, passes to the 

 lymphatic gland in the hollow of the shoulder, and to the 

 adjacent muscles ; it supplies the clavotrapezius, acromio- 

 trapezius, levator scapulae ventralis, splenius, occipitoscapularis, 

 and rhomboideus. A second branch passes between the sub- 

 scapularis and supraspinatus muscles, dividing into various 

 branches which supply the muscles named. The third branch 

 pierces the supraspinatus muscle, just craniad of the acromion 

 process, and ramifies in that muscle. 



