OF DIDELPHYS VIRGINIANA. 141 



grave objections arising from the position and relations of the latter muscle. At the same 

 time the psoas is not otherwise satisfactorily accounted for ; at any rate, I cannot regard it 

 as the "accessor}' short extensor" of the femur, nor see its homologue in the supraspi- 

 natus, as Professor Wilder has. Unless I misunderstand that writer's use of the terms, the 

 psoas is the "direct long flexor" of the femur — just the opposite. For the rest, there is 

 something to give color to the conjecture that the psoas and iliacus form one muscle, inas- 

 much as they have a common insertion, and similar function. 



Few anatomists will be disposed to deny the homology of the subscapularis and iliacus ; 

 their position being identical, their relations nearly the same ; and both having rotation 

 as a prominent feature of their action. They both belong, furthermore, to the "short" 

 flexor set, as "accessories." 



There are three large muscles upon the outer surfece of the scapular arch, all partly 

 overlapping each other, all acting upon the proximal extremity of the humerus. They are, 

 from before, backward, — deltoid, supraspinatus, infraspinatus. There are likewise three 

 upon the outside of the pelvic arch, corresponding in position, relation, and virtually in 

 function ; they are, in reversed direction, — from behind, forward, — ecto-gluttTeus, meso- 

 glutseus, ento-glutasus. These are readily acceptable as homologous ; in fact, it is not easy 

 to see how an opposite conclusion may be reached. In the case of the deltoid and ecto- 

 glutfeus, the correspondence extends to such an unusual degree as to be observable in the 

 texture of the muscular fascicles. It is difficult to say to what set or sets of muscles — 

 whether flexor or extensor, or long or short — these three muscles are morphologically re- 

 ducible ; the probability is, that they comprehend both. The glutaeus maximus is cer- 

 tainly both long and short in having sacral and iliac portions ; whUe the action of the 

 three together, both at shoulder and hip, is so complex — and particularly in the cases of the 

 spinati and two smaller glutsei — so varied in different animals, that they can hardly be said, 

 in general terms, to have any specifically determinate mode of operation. 



The teres major lies along the posterior border of the scapula, and is the short direct 

 flexor of the humerus. At the hij) there is a little muscle lying along the corresponding 

 (anterior) border of the ilium, and morphologically the short direct flexor of the femur ; 

 although its diminutive size — in fact, its almost rudimentary condition — precludes belief 

 that it is teleologically of much account. This is the muscle described (p. 125,) as ilio- 

 femoralis ; but which is undoubtedly the same as that described by Ti'aill, Wilder and 

 others in certain quadrumana, under the name of " scansorius." This seems to be the 

 homologue of the teres major. 



The teres minor is wanting in the opossum ; were it present I should be at a loss to 

 account for it. The glutaeus minimus, to which Prof Wilder compares it, has just been 

 otherwise homologized. It is an inconstant muscle, and it may not be going too far to 

 inquire whether it be really a morphological integer. The two rhomboidei, and the levator 

 anguli scapulae and serratus magnus of human anatomy are conclusively parts of each 

 other, not integers of themselves ; and similarly the teres minor may result from tele- 

 ological modification of one of the two muscles between which it lies. If it be referable 

 to the infra-spinatus, as seems likely, judging from its insertion, rather than to the teres 

 major, the difficulty vanishes ; for it is then correspondent to the glutaeus minimus. 



The way has grown smoother as we have advanced, until now, encountering the great 

 extensor bundles upon the front of the femur and back of the humerus, it is perfectly 



H2MOIBS HOST. BOC. NAT. HIST. TOL. n. 86 



