9 



BEANCHES OF THE SUBCLAVIAN AETEEY. 911 



(d) Tracheal branches are distributed to the trachea ; they anastomose with branches 

 rf the superior thyreoid and with' the bronchial arteries. 



(e) An inferior laryngeal branch, accompanies the recurrent nerve to the lower part 

 )f the larynx. It enters the larynx, at the lower border of the inferior constrictor, 



1 rives branches to its muscles and mucous membrane, and anastomoses with the laryngeal 

 aranch of the superior thyreoid artery. 



(/) The ascending terminal branch supplies the posterior and lower part of the 

 :hyreoid gland, and anastomoses with branches of the superior thyreoid artery. 



(g) The inferior terminal branch is distributed to the lower and medial part of the 

 3orresponding lobe of the thyreoid gland. It anastomoses with its fellow of the opposite 

 Me and with branches of the superior thyreoid artery. 



(B) Arteria Transversa Colli. The transverse cervical artery (Figs. 759 and 

 761) arises from the thyreo-cervical trunk and runs upwards and posteriorly across 

 the posterior triangle of the neck to the anterior border of the trapezius ; there 

 it divides into a ramus ascendens (O.T. superficial cervical) and a ramus descendens 

 'O.T. posterior scapular). It is very variable in size, and not infrequently the 

 ramus descendens arises separately from the third part of the subclavian. 



Immediately after its origin, under cover of the internal jugular vein, it crosses 

 , the scalenus anterior, lying superficial to the phrenic nerve and under cover of the 

 sterno-mastoid muscle; on the left side it is also crossed, superficially, by the terminal 

 part of the thoracic duct. Passing from beneath the sterno-mastoid, it enters the 

 ! lower part of the posterior triangle of the neck, where it lies upon the trunks of 

 the brachial plexus, and, as it runs upwards and backwards to its termination, it 

 passes medial to the posterior belly of the omo-hyoid. 



The ascending branch may be a separate vessel which springs from the thyreo-cervical trunk 

 and takes the course described, whilst the descending branch arises from the third part of the 

 subclavian artery and lies at a lower level. In such cases the upper of the two vessels is called 

 the superficial cervical artery and the lower the transverse cervical artery. If the superficial 

 cervical artery is absent it is replaced by the ascending branch of the transverse cervical. 



Branches. (a) Small muscular branches to the surrounding muscles. 



(6) The ascending branch, usually a slender branch, passes beneath the trapezius ; it 

 1 sends branches upwards and downwards, superficial to the levator scapulae and upon the 

 i splenius ; the ascending branches anastomose with the descending branch of the occipital 

 artery, and the descending branches accompany the accessory nerve and anastomose with 

 the descending branch and transverse scapular artery. 



(c) The descending branch runs downwards, deep to the levator scapulae and the 

 rhomboid muscles, close to the vertebral border of the scapula. It runs parallel with, 

 and a short distance away from, the dorsal scapular nerve (O.T. nerve to the rhomboid 

 1 muscles), and it sends branches into the supraspinous, the infraspinous, and the subscapular 

 fossae, which anastomose with branches of the transverse scapular and subscapular arteries. 

 It also sends branches backwards, through and between the rhomboid muscles, which 

 anastomose with the branches of the ascending division of the transverse cervical and 

 1 with the posterior branches of the intercostal arteries. 



(C) Arteria Transversa Scapulae. The transverse scapular artery (O.T. supra- 

 scapular) springs from the thyreo-cervical trunk and terminates in the infraspinous 



fossa of the scapula. As a rule it is smaller than the transverse cervical artery. 

 Commencing behind the internal jugular vein, it crosses the scalenus anterior 



'and phrenic nerve, and is covered superficially by the sterno-mastoid and the 

 anterior jugular vein ; on the left side it lies behind the termination of the thoracic 

 duct also. Continuing, laterally, behind the clavicle, and crossing superficial to the 

 third part of the subclavian artery and the cords of the brachial plexus, it reaches 

 the scapular notch and passes over the superior transverse ligament. Then it 



, descends, with the suprascapular nerve, through the supraspinous fossa and deep to 

 the supraspinatus muscle, and after passing through the great scapular notch, deep 

 to the inferior transverse ligament, it enters the infraspinous fossa, where it anas- 

 tomoses with the circumflex scapular branch of the subscapular artery and with 

 twigs of the descending branch of the transverse cervical artery. 



Branches. (a) Muscular, to the sterno-mastoid, the subclavius, and the muscles on 

 the dorsum of the scapula. 



(b) The medullary, a small branch to the clavicle. 



