XIII 



PHYLUM CHORDATA 



367 



body of the sternum, dorsal to the pectoralis, and sending its 

 tendon (sb. civ.'} through the foramen triosseum to be inserted 

 into the dorsal aspect of the hum ems. In virtue of this arrange- 

 ment, the end of the foramen acting like a pulley, the direction 

 of action of the muscle is changed, the backward pull of the tendon 

 raising the humerus. There are three tensor es patagii (tns. lg., tns. 

 ///'., tns. ace.), the action of which is to keep the pre-patagium tensely 

 stretched when the wing is extended. A similar muscle (tns. m. p) 

 acts upon the post-patagium. The muscles of the digits are 

 naturally much reduced. 



The muscles of the neck and tail are well developed, those of 

 the back are practically atrophied, in correspondence with the im- 



pel 



FIG. 980. Columba livia. The principal muscles of the left wing ; the greater part of the 

 pectoralis (pet.) is removed, car. st. cariua sterni ; cl. furcula ; cor. coracoid ; cor. br. br. coraco- 

 brachialis brevis ; cor. br. lg. coraco-brachialis longus ; cp. st. corpus sterni ; ext. cp. rd. extensor 

 carpi radialis ; ext. cp. vl. extensor carpi ulnaris ; rt. cp. v.l. flexor carpi ulnaris ; gl. c. glenoid 

 cavity ; hu. head of humerus ; /n/'. its distal end ; pet. pectoralis ; pet', its cut edge ; pet", its 

 insertion ; prn. br. pronator brevis ; prn. hi. pronator longus ; pr. ptgm. pre-patagium ; 

 pt. ptgm. post-patagium; sb. civ. sub-clavius ; sb. clr'. its tendon of insertion passing through 

 the foramen triosseum, and dotted as it goes to the humerus ; tns. ace. tensor accessories ; tits, 

 br. tensor brevis ; tns. Iff. tensor longus ; tns. in. p. tensor membranaj posteiioris alse. 



mobility of that region. In the leg certain of the muscles are 

 modified to form the perching mechanism. The toes are flexed 

 by two sets of tendons, deep and superficial. The deep ten- 

 dons of the three forwardly directed digits are formed by the 

 trifurcation of the tendon of a single muscle, the peronccus medius, 

 that of the hallux is derived from a separate muscle, the flexor 

 per for cms, which is joined by a slip from the peronseus medius. 

 Thus a pull upon one tendon flexes all the toes. When the leg 

 is bent, as the bird settles to roost, the flexion of the tarso- 

 metatarsus on the shank puts the flexor tendons on the stretch as 



