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 



FlG. 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. br, coraco-brachialis brevis; cor. br. Ig, cqraco-brach!alis 

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

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

 head of humerus; hu' , its distal end; pet, pectoralis; pet', its cut edge; pet", its 

 insertion; prn. br, pronator brevis; prn. Ig, pronatpr longiis; pr. ptgm, pre- 

 patagium; pt.ptgni, 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; tns. ace, tensor accessorius; tns. br, tensor brevis; tns. Ig, tensor 

 longus; tns. m. p, tensor membranae posterioris alae. 



that bone {cp. st), and from the clavicle \d), 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 (/V/') into the ventral aspect of the humerus 



