Limbs : Upper Limb 73 



by its outer attachment the line separating the infraspinous and teres surfaces : therefore 

 the origin of Infraspinatus reaches this line, and extends up along it for a considerable 

 distance. The two Teres muscles lie against the aponeurosis on this line, and the 

 Teres major in particular is very prone to extend its area of origin on to the aponeurosis, 

 thus lying partly superficial to Infraspinatus. Origin of Teres minor extends to the 

 neck of the bone, its area being interrupted by the passage of the dorsalis scapulae 

 vessels : these lie in a definite groove on the bone, and are covered by a fibrous arch 

 from which muscle fibres arise. At the inner end of the groove there is a break in the 

 ridge for the infraspinous aponeurosis, showing where the vessels pierce the aponeurosis 

 to pass deep to the Infraspinatus, and this point can be used as the upper limit of 

 origin of the outer border of Infraspinatus. 



By articulating the bones it can be seen that the lower border of Teres minor 

 comes down below the level of the axillary border of the bone, as in the case of Sub- 

 scapularis, and almost to the same extent. In other words, the two muscles are only 

 partly separated by the bone, and below this, from within outwards, by dorsalis 

 scapulae artery, long head of Triceps, and finally by the upper end of the humerus. 



Teres major is a part of the Subscapular mass which has extended round the border of the bone 

 to reach its dorsal surface, but, being part of that mass, it must lie in the same general plane that 

 is, it lies along the lower border of Subscapularis and passes with it in front of Triceps, instead of 

 behind the plane of this muscle which would be the level of muscles belonging properly to the dorsal 

 musculature of the scapula. It is not separated from its main mass as a result of its dorsal origin 

 or the passage of nerves and vessels between them, but owing to its difference in function : this is 

 the great cause of separation between muscles belonging to the same mass fundamentally. 



The spino-glenoid ligament, which bridges over the great scapular notch, is simply a fascial band 

 made by the fusion of the fascial sheaths of Supj-aspinatus and Infraspinatus : these coverings are 

 at first separated by the spine, but they come "together at the free edge of this process, and are 

 attached to this edge and to the capsule, etc., further out. The fused sheaths thus form a " liga- 

 ment " with these connections, and this must of course be over the vessels and nerve here, because 

 they are deep to the plane of the muscles and fasciae concerned. 



Spine and Acromion. 



This has a thick rounded bar at its free outer border, which is the only part of the 

 process to be preformed in cartilage (Fig. 58). The remaining thinner portion is 

 apparently ossified directly in membrane, which represents probably the distal attach- 

 ment of part of the Trapezius. 



The upper and lower borders are continued behind into the aponeurotic rims for 

 the spinatus muscles on the vertebral edge : this indicates that the covering aponeuroses 

 are attached to the spine. Examine the areas for Trapezius and Deltoid : in both 

 cases they spread on to the superficial surface of the bone for some distance, but in 

 the case of the Deltoid the area narrows to the line of the border in its inner half, 

 and so corresponds with the fact that the most posterior fibres of the Deltoid are 

 aponeurotic, lying on and fused with the infraspinous aponeurosis, and extending on 

 this nearly to the vertebral border of the bone. The Trapezius area extends in along 

 the spine till it lies above the deltoid tubercle, where it narrows and turns downwards 

 and outwards, forming a hook-shaped roughened ridge. This arrangement of the 

 insertion which is really responsible for the existence of the " deltoid tubercle " 

 is due to the'convergence of the fibres of Trapezius (Fig. 59), which would otherwise 

 be twisted and overlap one another as they reached their insertion. The inner part 

 of the spine is covered by Trapezius, which plays over it, and a small bursa may be 

 found here very occasionally. The angle of the acromion overhangs the Infraspinatu?, 



