MUSCULAR SYSTEM. 85 



limited to a smaller proportional extent, namely, about one eighth of 

 the anterior and outer part of the ^ternum ; it is inserted by a 

 feeble tendon into the crest of the humerus, which it moves in the 

 direction forward. In the Penguin and some other Palmipedes trie 

 second pectoral muscle is actually the largest and strongest of the 

 three, and extends over the whole length of the sternum ; the pec- 

 toralis tertius s. coraco-lracliialis inferior is here, also (arid partic- 

 ularly in the Gallinac), strongly developed ; it acts likewise as a de- 

 pressor of the humerus, and thus these muscles become in birds 

 which, like the Penguin, use their wings only as fins, no less import- 

 ant agents in the performance of that function, than in the ordinary 

 one of flight. The muscles of the shoulder are more feebly de- 

 veloped ; the deltoid is divided into several portions ; the rest may be 

 easily distinguished as the analogues of the trapezius, rhomboideus, 

 supra spinatuSj infra-spinatus and sulscapularis of the human sub- 

 ject. The extensors of the alary membrane (m. m. extensores plica 

 alaris anterioris) present a peculiar structure ; they consist of sev- 

 eral short muscular bellies, which arise from the furcular, coracoid 

 and humeral bones, and give off long slender tendons, one of which, 

 composed partly of elastic tissue, runs along the free anterior border 

 of the aponeurotic expansion of the wing, and is inserted into that 

 portion of it which covers the radial side of the carpal bones. A 

 similar tendon, only feebler and shorter, lies in the posterior part of 

 the alary expansion (in. tensor plica alaris posterioris], and is given 

 off by a muscle arising from the ribs ; it is inserted by an aponeurosis 

 into the fascia of the fore-arm. 



Birds have in general two flexor muscles of the fore-arm, of which 

 the biceps is strongly developed, and a single extensor ; they have 

 also pronators and supinators, but their action is limited to inflexion 

 and extension of the fore-arm. Long narrow-bellied muscles with 

 thin -tendons are also met with, which adduct and abduct the hand, 

 as well as move the phalanges of the digits ; they have received 

 the names of m. m. extensores et flexores carpi s. mctacarpi radiales et 

 ulnares (longus et brevis), m.m. extensores, flexores, abductores, adduc- 

 tores poll-ids et digiti medii, &c. The last muscles act only as ex- 

 tensors and abductors. 



The muscles of the pelvis are very slightly developed, and there 

 are none which might correspond to the psoas, obturator externus 

 and quadratus lumborum muscles ; the other muscles here situated 

 may be compared with the iliacus, obturator internus and pectin<Bus. 

 In the posterior extremities, from their having to support the entire 



