12 ANATOMY OF VERTEBRATES. 



In claviculate marsupials the deltoid is larger, and consists of 

 three fasciculi. 



The teres major is a strong sub-compressed muscle arising from 

 near the posterior half of the inferior costa of the scapula, and 

 joining, as before stated, the tendon of the latissimus. 



The triceps extensor has its long portion arising from the anterior 

 third of the inferior costa of the scapula ; its second head comes 

 from the posterior part of the proximal third of the humerus ; the 

 third portion takes its origin from the whole of the posterior part 

 of the humerus ; in addition to these, the olecranon receives the 

 above-described fourth superadded slip from the latissimus dorsi. 



The pectoralis major is, as usual in the Marsupial and many 

 higher quadrupeds, a complicated muscle ; it consists of an anterior 

 or superficial and a posterior or deeper portion ; the anterior portion 

 receives the strip of fibres before mentioned from the trapezius, 

 there being no clavicle or clavicular ossicle interposed in the Pe- 

 rameles ; its fibres converge, increasing in thickness as they 

 diminish in breadth, and are inserted into the anterior and outer 

 part of the strongly developed pectoral ridge. The second and 

 main portion of the pectoralis arises from the whole extent of the 

 sternum ; its fibres are twisted obliquely across each other as they 

 converge to be inserted into the inner part of the pectoral ridge ; 

 some of the internal and posterior fibres of this portion of the 

 twisted pectoral pass obliquely upward and behind the anterior 

 fasciculi, and are inserted into the coracoid process, thus repre- 

 senting the pectoralis minor. Beneath this latter portion of the 

 pectoral, a long and slender muscle passes to be inserted into 

 the anterior part of the tuberosity of the humerus ; this may 

 likewise be regarded as a dismemberment of the pectoralis major, 

 but it arises from the fascia of the rectus abdominis, below the car- 

 tilages of the lower ribs. Thus the strong pectoral ridge of the 

 humerus is acted upon by muscles having a range of origin from 

 the occiput and cervical vertebra? along the whole extent of the 

 chest to the beginning of the abdomen. 



The biceps is a powerful muscle, although its short head from 

 the coracoid process is suppressed. The long head has the usual 

 origin and relation to the shoulder-joint ; its tendon is very thick 

 and short. The fleshy belly joins that of the strong brachialis in- 

 ternus, situated at the external side of the humerus, whence it 

 takes its principal origin from the short deltoid ridge, closely con- 

 nected there with the second portion of the triceps, and deriving 

 some fleshy fibres from the lower and outer third of the humerus. 

 The portion of the biceps arising by the long head soon resolves 



