312 SHOULDER-GIRDLE IN MONOTREMES, 



scapular part of the deltoid ; anteriorly by the origin of the infra- 

 spinatus and upper two-thirds of the glenoid border and upper 

 part of the triceps tendon ; posteriorly by the upper half of the 

 posterior border. In addition to this the muscle arises by a still 

 more extensive origin from the inner surface of the scapula, the 

 area being bounded dorsally by a ridge close to the vertebral 

 border on which is inserted the serratus magnus ; anteriorly by 

 the true anterior costa on which is inserted part of serratus 

 magnus, and posteriorly by the upper half of the (actual) posterior 

 border of the scapula. 



Insertion. The muscle runs downwards and inwards to 

 be inserted on the distal extremity of the lesser tuberosity, and 

 on a " sesamoid bone "* situated on the summit of the lesser 

 tuberosity, close to the shoulder joint, being closely related to the 

 insertion of the epicoraco-brachial antero-internally, and teres 

 minor on the posterior face of the humerus. 



Innervation. Echidna et Ornithorhynchus : N. subscapn- 

 laris, from iv., v., vi. cervical nerves. 



Westling : the same for Echidna. 



Echidna. 



Westling describes this muscle as arising from the hinder and 

 upper (vertebral) part of the dorsal surface of the scapula, and its 

 insertion into the summit of the tuberculum minus humeri. 



Leche follows Westling. 



MiVART says — " This large muscle has an anomalous situation, 

 inasmuch as it is confined to the outer surface of the scapula. It 

 arises, indeed, from the wjiole of the outer surface posterior to the 

 origin of the long head of the triceps." He remarks, that, "in 

 the Ornithorhynchus this muscle takes origin in part from the 

 outer surface of the scapula, but mainly from the inner face in 

 the usual mode." 



* This so-called sesamoid bone corresponded exactlj' in position and 

 relations to the epiphysis of the lesser tuberosity of the humerus of a young 

 Echidna, in the writer's possession. [Vidt fig. 18, L.T.). 



