364 



AZYGOS. 



it arrives at the acromial end of that bone, 

 where it is expended in a number of branches 

 which go to supply the scapulo-clavicular and 

 scapulo-humeral articulations, and also the 

 supra-spinatus and deltoid muscles. This ar- 

 tery anastomoses with the supra-scapular and 

 posterior circumflex in the vicinity of the acro- 

 mion process. The inferior or cephalic branch 

 descends in company with the cephalic vein in 

 the cellular interval between the deltoid and 

 pectoralis major muscles, and is distributed to 

 these muscles and the integuments. 



2. The superior thoracic (thorucica suprema, 

 Seem.) is very irregular as to the place of its 

 origin, coming as frequently from the acromial 

 as from the trunk of the axillary; it passes ob- 

 liquely forwards between the greater and lesser 

 pectoral muscles, and divides into several 

 branches, which are distributed to these two 

 muscles, the integuments, and more deeply to 

 the serratus magnus and the two or three supe- 

 rior intercostal muscles, anastomosing with the 

 intercostal and internal mammary arteries. 



3. The inferior thoracic (thoracica longior 

 or nwmmaria externa) is subject to the same 

 variety of origin as the superior thoracic; it 

 sometimes arises from the subscapular. This 

 artery descends on the surface of the serratus 

 magnus muscle along the inferior border of the 

 pectoralis major; its branches are distributed 

 to the glands and cellular tissue of the axilla, 

 to the serratus magnus, and pectoralis major 

 and minor, and the intercostal muscles ; it also 

 supplies the mammary gland and the integu- 

 ments ; it anastomoses with the intercostal, in- 

 ternal mammary, superior thoracic, and sub- 

 scapular arteries. 



Soemmerring describes a fourth thoracic ar- 

 tery, under the name of alar is sive axillaris 

 glandulosa,* which is distributed principally to 

 the axillary lympathic glands; this artery is 

 very irregular in its origin, sometimes coming 

 from the trunk of the axillary artery, and as 

 often arising from the thoracica longior or the 

 subscapularis. Instead of a single artery going 

 to the glands of the axilla, these parts are more 

 visually supplied by several small twigs which 

 arise from the arteries in their vicinity. 



4. The subscapular artery is generally the 

 largest branch of the axillary ; it arises at the 

 lower edge of the subscapularis muscle, lying 

 at its origin behind the brachial plexus; it gives 

 three or four branches to the glands and cellular 

 tissue of the axilla and to the subscapularis 

 muscle, after which it divides into two branches, 

 one inferior, the smaller, the other, larger, called 

 the external scapular. The inferior branch de- 

 scends along the inferior border of the subsca- 

 pularis muscle and the inferior costa of the 

 scapula between the latissimus dorsi and the 

 serratus magnus, to which muscles, the 

 teres major, and the integuments it is finally 

 distributed, anastomosing with the posterior 

 scapular artery at the inferior angle of the 

 scapula. The external branch, circumflexus 

 scapula of Soemmering, passes backwards 

 through a triangular space formed by the sub- 



* De Hum. Corp. Fab. t. v. p. 189. 



scapularis above, the teres major inferiorly, and 

 the tendon of the long head of the triceps ex- 

 ternally, and after having given several branches 

 to these muscles, it divides into two branches, 

 a superficial and a deep-seated ; the superficial 

 branch is distributed to the teres major, teres 

 minor, infra-spinatus, latissimus dorsi, and the 

 integuments; the deep-seated branch winds 

 round the neck of the scapula under the teres 

 major, and entering the fossa infra-spinata, 

 supplies the infra-spinatus muscle, the scapula, 

 and the scapulo-humeral articulation. This 

 branch anastomoses freely with the branch of 

 the supra-scapular, which descends under the 

 root of the acromion process. 



5. The posterior circumflex, next to the sub- 

 scapular, is the largest branch of the axillary 

 artery, from the posterior side of which it arises; 

 frequently it comes from the infra-scapular. It 

 passes backwards through a quadrilateral space, 

 bounded in front by the neck of the humerus, 

 behind by the long head of the triceps, above 

 by the subscapularis, and below by the teres 

 major; coursing round the neck of the humerus, 

 it passes below the inferior edge of the teres 

 minor, and attaching itself to the under surface 

 of the deltoid, is principally distributed to that 

 muscle, giving branches in its course to the 

 capsular ligament of the shoulder-joint, the 

 subscapularis, teres major and minor, infra- 

 spinatus, and triceps; it anastomoses with the 

 supra-scapular and acromial thoracic by branches 

 which it sends to the acromion, and with the 

 anterior circumflex by the branches which it 

 gives to the articulation of the shoulder. 



6. The anterior circumflex is a very small 

 vessel, arising either from the axillary or the 

 posterior circumflex ; it passes forwards round 

 the neck of the humerus under the coraco-bra- 

 chialis and short head of the triceps, to both of 

 which muscles it gives branches; arriving at the 

 bicipital groove, it sends off several branches, 

 some of which descend along that groove, and 

 others spread over the surface of the head and 

 neck of the humerus, supplying that part of 

 the bone and the tendons which are inserted 

 into its tuberosities ; while the continuation of 

 the vessel entering the bicipital groove ascends 

 by the side of the tendon of the long head of 

 the biceps, passes under the capsular ligament, 

 to which and the other parts entering into the 

 formation of the shoulder-joint it is ultimately 

 distributed. This artery anastomoses with the 

 posterior circumflex and ascending branches of 

 the superior profunda of the brachial artery. 



For the Bibliography see that of ANATOMY 

 (INTRODUCTION) and of ARTERY. 



(J. Hart.) 



AZYGOS, (, vyo$, jugum.) The term 

 azygos is applied by anatomical writers to cer- 

 tain parts of the human body, which, being 

 situated in or near the mesial line, appear 

 singly, and not symmetrically or in pairs : 

 thus we read of the azygos process of the 

 sphenoid bone, of the azygos uvula muscle, 

 of the azygos artery, vein, &c. This term, 

 however, (strictly speaking,) is seldom very 

 correctly applied, for in the cases of the bony 



