SHOULDER SCAPULAR REGION 77 



two lamellae a superficial and a deep, which, as they pass 

 forwards, enclose between them the deltoid muscle. 



Dissection. Place a small block in the axilla, fix the scapula 

 to it with hooks and bend the arm over the block to make the 

 fibres of the deltoid tense. Detach the lateral brachial cutaneous 

 branch of the axillary nerve from the deep fascia, and turn it 

 backwards to the point where it curves round the posterior 

 border of the deltoid ; then clean the deltoid. On the left side 

 commence at its posterior border, make an incision through the 

 deep fascia along the whole length of that border and reflect the 

 deep fascia forwards. On the right side commence in front, 

 where the fascia has already been partly reflected during the 

 dissection of the axillary region, and reflect the fascia backwards. 



M. Deltoideus. The deltoid muscle is composed of 

 short, coarse fasciculi, and as its name implies it is of 

 triangular form. Its proximal end or base arises : (i) from 

 the anterior border and the adjacent part of the upper 

 surface of the lateral third of the clavicle ; (2) from the 

 lateral border of the acromion ; and (3) from the inferior 

 lip of the posterior border of the spine of the scapula. Its 

 origin corresponds closely with the insertion of the trapezius. 

 Its fasciculi converge rapidly as they pass distally to the 

 pointed tendinous insertion on the rough deltoid tubercle 

 situated in the middle of the antero- lateral surface of the 

 body of the humerus (Fig. 45). The muscle is an abductor, 

 and a medial and lateral rotator of the humerus, and it is 

 supplied by branches of the anterior division of the axillary 

 nerve which enter its deep surface. 



Dissection. Place the limb on its posterior aspect. Release 

 the axillary vessels, and the nerves, from the coracoid process and 

 clean the angle between the humerus and the scapula. Follow 

 the axillary nerve and the posterior circumflex humeral artery 

 backwards. They will be found to enter a cleft between the 

 subscapularis above and the teres major below. Separate those 

 muscles and a triangular interval will be displayed. It is bounded 

 laterally by the surgical neck of the humerus. Crossing the space 

 from above downwards, behind the subscapularis and the teres 

 major is the long head of the triceps. It divides the triangular 

 interval into a lateralpart called the quadrangular space and a 

 medial part called the triangular space. The axillary nerve and 

 the posterior humeral circumflex artery pass through the quad- 

 rangular space. Now reverse the limb, push the posterior 

 border of the deltoid forwards and find the axillary nerve and 

 the posterior humeral circumflex artery. They emerge from 

 the quadrangular space and pass forwards round the lateral 

 surface of the surgical neck of the humerus. 



At this stage of the dissection the deltoid muscle must be 

 reflected. Cut it away from its origin from the clavicle, acromion, 



