PHYLUM CHORDATA 



473 



wing, by which the bird rises into and propels itself through 

 the air, is performed by the pectoralis (Fig. 286, pet), an 

 immense muscle having about one-fifth the total weight of 

 the body; it arises from the whole of the keel of the 

 sternum {car. si), from the posterior part of the body of 



Fig. 286. — Columba livia. The principal muscles of the left wing; the greater 

 part of the pectoralis {pet) is removed, car. st, carina sterni; cl, furcula; cor, 

 coracoid; cor. br. or, coraco-brachialis brevis; cor. br. Ig, coraco-brachalis 

 longus; cp. st, corpus sterni; ejrt. cp. rd, extensor carpi radialis; ext. cp. nl, 

 extensor carpi ulnaris; Jl. cp. ul. flexor carpi ulnaris; gl. c, glenoid cavity; hu , 

 head of humerus; hit , its distal end; pet, pectoralis: pet', its cut edge: /£■/", its 

 insertion; prn. br, pronator brevis; prtt. Ig, pronator longus; pr.ptgm, pre- 

 patagium; pt.ptgm, post-patagium; sb ch>, sub-clavius; sb. civ , its tendon of 

 insertion passing through the foramen triosseum, and dotted as it goes to the 

 humerus; tits, ace, tensor accessorius; tns. br, tensor brevis; ins. Ig, tensor 

 longus; tus. m. p, tensor membranse posterioris alse. 



that bone {cp. st), and from the clavicle {cl), filling nearly 

 the whole of the wedge-shaped space between the body 

 and the keel of the sternum, and forming what is commonly 

 called the "breast" of the bird. Its fibres converge to 

 their insertion {pet") into the ventral aspect of the humerus 



