282 SHOULDER-GIRDLE IN MONOTREMES, 



the origin in placed ventral to the insertion of the anterior part of 

 the trapezius on the clavicle and acromion. As noted above, the 

 antero-internal border is separated from the P. major by a cellular 

 interval. 



Origin, (b) Scapular jjortioyi. — This muscle arises from the 

 anterior two-fifths of the external edge of the vertebral border, and 

 slightly from the adjoining external surface of the scapula; and 

 from the upper one-third of the outer border of the spine. (Fig. 

 12, Dlt. S.). 



Insertion. The muscle, arising fleshy, runs downward and 

 outwards. As it approaches its insertion it suddenly develops a 

 narrow tendon, and disappearing beneath the outer border of the 

 clavicular deltoid, is embraced between the layers of that muscle, 

 and then becomes inserted on a tubercle situated about the mid- 

 point of the pectoro-deltoid ridge. (Fig. 8, Dlt. S.). 



Relations. At its origin a few fibres are placed superficial 

 to the tendon of insertion of the posterior trapezius, but the fibres 

 which arise from the vertebral border of the scapula are hidden 

 by the trapezius. The origin from the spine is closely related to 

 the insertion of the anterior trapezius. The muscle hides from 

 view the infraspinatus and part of the origin of the long head of 

 the triceps. 



Innervation. Clavicular portion : N. axillaris and possibly 

 a minute twig from the N. supracoracoideus. Scapular portion : 

 N. axillaris. (Both animals). 



Westling — Echidna: "N. axillaris; ausserdem giebt der Eamus 

 ciitaneus n. supracoracoidei einen sehr feinen Faden zum M. 

 deltoideus I. ab." In Ornithorhynclbus Westling refers to her 

 figure (Fig. 17, rs.), and states that among the branches given off 

 from this chord is— "einen (N. suprascapularis ?) fiir den M. infra- 

 spinatus, den obern Theil des M. pectoralis major {i.e., clavicular 

 deltoid) und den M. supraspinatus gemeinsamen Kerven, und 

 einen (N. axillaris) fUr die hintere Portion der M. deltoideu.s." 



