THE SUPRASCAPULAR ARTERY. 425 



Varieties. The inferior thyroid artery occasionally arises as an independent branch from 

 the subclavian ; rarely from the common carotid or the vertebral. The primary division of 

 the artery often takes place behind the common carotid, and in rare cases there are two 

 inferior thyroid arteries arising 1 separately from the subclavian. The artery, or one of its 

 divisions, has been seen crossing in front of the common carotid artery. A considerable 

 branch often passes forwards around the upper end of the trachea to the fore part of the 

 thyroid body. The inferior thyroid artery varies much in size, and occasionally is altogether 

 wanting. The several thyroid arteries are developed in inverse proportion to one another, 

 diminution or absence of one being compensated for by an increased size of the others, or by 

 an accessory artery, the thyroidea ima (p. 388). 



The ascending cervical artery is occasionally derived from the subclavianjDr from one of 

 the other branches of that vessel, as from the transverse cervical or the suprascapular. It is 

 sometimes much larger than usual, and takes the place of the occipital artery. A branch 

 from it not unf requently compensates for the small size of the deep -cervical artery. 



B. The suprascapular artery (iv) (transverse scapular, or transverse humeral) 

 arises from the thyroid axis, and courses from within outwards, being deeply placed 

 at the root of the neck. At first it descends obliquely towards the clavicle, resting 

 upon the scalenus anticus, and covered by the sterno-mastoid muscle ; it then crosses 

 the subclavian artery, and runs transversely outwards behind and parallel with the 

 clavicle to the upper border of the scapula, where it is joined by the suprascapular 

 nerve. Here the nerve passes through the suprascapular notch and beneath the 

 ligament of the same name, but the artery usually crosses over that band, and inclin- 

 ing downwards enters the supraspinous fossa. It gives off branches which ramify 

 beneath the supraspinatus muscle, and is then continued down behind the neck of 

 the scapula into the infraspinous fossa, where it terminates by anastomosing with 

 the dorsal and posterior scapular arteries. 



Branches. (a) Muscular branches to the sterno-mastoid, subclavius, and other 

 neighbouring muscles. 



(#) A suprasternal twig crosses the inner end of the clavicle and is distributed 

 to the skin at the upper and mesial part of the chest. 



(c) The medullary artery of the clavicle enters the canal on the posterior surface 

 of that bone. 



(d) The supra-acromial branch passes outwards through the attachment of the 

 trapezius to reach the surface of the acromion, on which it ramifies, anastomosing 

 with offsets from the acromio- thoracic artery. 



(e) A small subscapular branch, given off as the artery passes over the notch , 

 anastomoses with the posterior scapular and subscapular arteries in the subscapular 

 fossa and substance of the subscapularis muscle. 



(/) Branches enter the dorsal scapular muscles, the bone and shoulder-joint. 



Varieties. The suprascapular? artery in some cases springs independently from the 

 second or third part of the subclavian ; or it may arise from that vessel by a common 

 trunk with the transverse cervical or posterior scapular, or more rarely with the internal 

 mammary. It has also been found to proceed from the axillary artery, and from the 

 subscapular branch of that vessel. This artery is sometimes very small, in which case 

 the deficiency is supplied by a branch of the posterior scapular or by the dorsal scapular 

 artery. 



C. The transverse cervical artery, the third branch of the thyroid axis 

 passes outwards a short distance above the clavicle, and therefore higher than the 

 suprascapular artery. It crosses over the scaleni muscles and the brachial plexus, 

 sometimes passing between the nerves of the latter, and is crossed by the omo-hyoid 

 muscle. Beneath the upper margin of the trapezius, and near the anterior edge of 

 the levator anguli scapulae, it divides into two branches, the superficial cervical and 

 the posterior scapular. 



The superficial cervical artery (v) ascends beneath the trapezius, and distributes 

 branches to that muscle, the levator anguli scapulas and splenius muscles, as well as 



