436 



SCAPULAR REGION. 



By the removal of so much of these super- 

 ficial muscles as encroach on the scapular re- 

 gion, and of the strong fascia already de- 

 scribed, the deeper seated muscles of the 

 infra-spinal fossa, viz. the infra-spinatus and the 

 teres major and minor, are completely exposed. 



The infra-spinatus muscle arises from the 

 upper four-fifths of the dorsum of the scapula 

 below its spine. The strong fascia of invest- 

 ment already described also furnishes an 

 extensive surface of origin to its fibres ; the 

 muscle is triangular, the fibres all converging 

 anteriorly to their common tendon, which, 

 passing beneath the spine of the scapula and 

 the acromion process, approximates closely 

 to the tendon of the supra-spinatus muscle, 

 and is inserted immediately beneath it, into 

 the great tuberosity of the humerus. 



The teres minor muscle seems to be little 

 else than a fasciculus of the last described 

 muscle, to which it is parallel, and along the 

 lower edge of which it is placed : anteriorly, it 

 is inserted by a separate tendon into the 

 lowest portion of the great tuberosity of the 

 humerus. The teres minor and infra-spina- 

 tus muscles might be regarded as different 

 portions of one and the same muscle, not only 

 from the similarity of their anatomical rela- 

 tions, but also from the identity of their 

 physiological functions; both draw down- 

 wards and backwards the humerus, and pro- 

 duce the rotation outward of the arm at the 

 shoulder joint. The teres minor is placed 

 between the infra-spinatus superiorly and the 

 teres major inferiorly, in close contact with 

 the former, from which an aponeurotic septum 

 and branches of blood-vessels alone separate 

 it ; whilst a very considerable space, containing 

 the long head of the triceps, and some im- 

 portant nerves and vessels, intervenes between 

 it and the teres major. 



The teres major and the teres minor mus- 

 cles arise close together from the lowest 

 portion of the dorsum of the scapula. The teres 

 major (the more superficial of the two at its 

 origin) is attached to the rough surface on 

 the outer aspect of the inferior angle of the 

 scapula, whilst the teres minor arises more 

 anteriorly, from a narrow but well-marked 

 groove, situated just above the axillary margin 

 of the bone. At their origin the teres minor 

 is concealed by the teres major, but as they 

 pass towards the humerus they gradually 

 diverge, and are inserted on different aspects 

 of the bone, and at different levels, so that 

 the long head of the triceps firstly, and the 

 neck of the humerus secondly, intervene be- 

 tween them. The teres minor is inserted on 

 the outside of the humerus into its great 

 tuberosity, below the insertion of the infra- 

 spinatus muscle, whilst the teres major, in 

 company with the latissimus dorsi, passes on 

 the inner aspect of the humerus, and is in- 

 serted along with it into the bottom of the 

 bicipital groove: at their insertion, the tendon 

 of the teres major is posterior, and a little 

 inferior to the tendon of the latissimus dorsi. 



The teretes muscles, in diverging to the 

 humerus, form with the upper part of that 



bone a triangular space, of which the base is 

 at the humerus, and the apex at the inferior 

 angle of the scapula. The scapular origin of the 

 triceps extensor muscle in its vertical course 

 down the arm, crosses this space, and divides 

 it into compartments, a posterior triangular, 

 and an anterior quadrilateral one, through both 

 of which the axillary cavity communicates 

 with the posterior region of the scapula and 

 shoulder. 



The triangulir compartment, overlapped 

 posteriorly by the deltoid muscle, is bounded, 

 above, by the teres minor and axillary edge of 

 the scapula; below, by the teres major. Its base, 

 situated externally, is formed by the long head 

 of the triceps; whilst its apex, directed inter- 

 nally, corresponds to the point of contact of 

 the teretes muscles, where they arise together 

 from the scapula. In this compartment is 

 seen the posterior branch of the sub- scapular 

 artery (circumflexus scapulce, Soemmering), 

 forming here a curve, the convexity of which 

 is directed downwards and backwards. The 

 artery leaves this space by bending upwards 

 and backwards, beneath the teres minor and 

 infra-spinatus muscles. It thus arrives in the 

 infra-spinal fossa, lies next the bone, and 

 ramifying minutely anastomoses, superiorly 

 with the descending branch of the supra- 

 scapular artery, and posteriorly with the 

 termination of the posterior scapular artery. 

 (Vide AXILLARY ARTERY.) 



The quadrilateral compartment is bounded 

 above, by the capsular ligament of the shoulder 

 joint, by the prominence of the head of the 

 humerus, and by the tendinous attachments 

 of the teres minor and of the sub-scapularis 

 muscles ; below, by the teres major and latissi- 

 mus dorsi; externally, by the neck of the 

 humerus ; whilst, internally, it is separated 

 from the triangular compartment last de- 

 scribed by the long head of the triceps muscle; 

 it transmits, from within outwards, the circum- 

 flex nerve and posterior circumflex artery. 

 This artery contributes to form the great 

 scapular anastomosis ; some of its branches 

 ascending in the substance of the deltoid 

 muscle, inosculate freely with the superior 

 acromial branches of the infra-scapular artery, 

 whilst others pass backwards and unite in the 

 infra-spinal fossa, with branches of the sub- 

 scapular and the posterior scapular arteries. 

 The circumflex nerve is distributed almost 

 exclusively to the deltoid muscle ; but two 

 collateral branches are detached from it, which 

 are distributed in the scapular region; the first, 

 a branch to the teres minor muscle ; the 

 second, a cutaneous filament, which escapes 

 from beneath the posterior edge of the deltoid 

 muscle, and is distributed to the integument. 



The posterior scapular artery, although 

 placed beyond the limits of the scapular 

 region, may, nevertheless, be here described, 

 as it is distributed chiefly to the parts con- 

 tained within it. Under the name of "trans- 

 versalis colli" this artery arises in the neck 

 from the thyroid axis, near to, arid sometimes 

 by a common trunk with, the transversalis 

 humeri ; it sometimes comes from the sub- 



