564 THE BLOOD-VASCULAR SYSTEM 



2. THE THYREOCERVICAL TRUNK 



The thyreocervical trunk [truncus thyreocervicalis] or thyreoid axis arises from 

 the upper and front part of the subclavian artery, usually opposite the internal 

 mammary, and slightly medial to the scalenus anterior. It is a short thick trunk, 

 and divides almost immediately into three radiating branches — namely, the 

 inferior thyreoid, the transverse scapular, and the transverse cervical (figs. 444, 

 457). This is the usual form only on the left side (see page 559). It may give off 

 also the ascending cervical. 



THE INFERIOR THYREOID ARTERY 



The inferior thyreoid artery [a. thyreoidea inferior] is the largest of the three 

 branches into which the thyreocervical trunk (thyreoid axis) divides, and may 

 arise in a common trunk with the transverse scapular, or as a branch of the sub- 

 clavian. It ascends tortuously passing medially in front of the vertebral artery, 

 the inferior laryngeal nerve and the longus coUi muscle, and behind the common 

 carotid and the sympathetic nerve or its middle cervical ganglion, to the thyreoid 

 gland, where it anastomoses with the superior thyreoid artery and the artery of the 

 opposite side. 



The branches of the inferior thyreoid artery are : — (1) Muscular; (2) CBsophageal 

 and pharyngeal; (3) tracheal; (4) inferior laryngeal; (5) glandular; and (6) as- 

 cending cervical. 



(1) The muscular branches supply the scalenus anterior, longus coUi, sternohyoid, sterno- 

 thyreoid, and omo-hyoid muscles, and the inferior constrictor muscle of the pharynx. 



(2) The oesophageal and pharyngeal branches [rami cesophagei et pharyngei] of the inferior 

 thyreoid artery supply the oesophagus and pharynx and anastomose with the other arteries 

 supplying those structures. 



(3) The tracheal branches [rami tracheales] ramify on the trachea, where they anastomose 

 with the tracheal branches of the superior thyreoid and bronchial arteries. 



(4) The inferior laryngeal artery [a. laryngea inferior] passes along the trachea to the back 

 of the cricoid cartilage in company with the inferior laryngeal nerve. It enters the larynx 

 beneath the inferior constrictor. Its further distribution in that organ is described under 

 Larynx. 



(5) The glandular branches [rami glandulares] supply the thyreoid gland. 



(6) The ascending cervical artery [a cervicalis ascendens] (figs. 444, 457) is given off from 

 the thyreocervical trunk or from the inferior thyreoid as that vessel is passing beneath the 

 carotid sheath. It ascends between the scalenus anterior and the longus capitis (rectus capitis 

 anterior major), lying parallel and medial to the phrenic nerve and behind the internal jugular 

 vein. It anastomoses with the vertebral, ascending pharyngeal, and occipital arteries, and 

 supplies branches to the deep muscles of the neck [rami musculares], to the spinal canal [rami 

 spinales], and to the phrenic nerve. Two veins accompany the ascending cervical artery and 

 end in the innominate vein. 



THE TRANSVERSE SCAPULAR ARTERY 



The transverse scapular or suprascapular [a. transversa scapulae] artery passes 

 laterally across the root of the neck, lying first beneath the sterno-mastoid, and 

 then in the subclavian triangle behind the clavicle and subcalvius muscle. At 

 the lateral angle of this space it is joined by the suprascapular nerve, sinks 

 beneath the posterior belly of the omo-hyoid, and passes over the ligament bridg- 

 ing the scapular notch, the nerve passing through the notch (fig. 461). It then 

 ramifies in the supraspinous fossa of the scapula, and, winding downward round 

 the base of the spine over the neck of the scapula, enters the infraspinous fossa, 

 and terminates by anastomosing with the circumflex (dorsal) scapular artery, 

 and the descending branch of the transverse cervical (posterior scapular) artery. 



As it lies under cover of the sterno-mastoid muscle, it crosses the phrenic nerve and the 

 scalenus anterior; and as it courses through the subclavian triangle, it is separated by the 

 cervical fascia which descends from the omo-hyoid to the first rib, from the subclavian artery 

 and brachial plexus of nerves. If this artery is seen in tying the subclavian it should not be m 

 injured, as it is one of the chief vessels by which the collateral circulation is carried on after | 

 ligature of the subclavian in the third part of its course. At the lateral part of the subclavian 

 triangle it is covered by the trapezius, and after passing over the transverse scapular ligament 

 it pierces the supraspinous fascia and passes beneath the supra-spinatus muscle, ramifying 

 between it and the bone. In the infraspinous fossa it lies between the infra-spinatus and 

 the bone. The artery is accompanied by two veins. 



