OF THE SOUTHERN APTERYX. 299 



manifests the proportions, as compared with the glutcsus medius, which the muscle to 

 which I have assigned the name ol" glutaus externus in the Apteryx, presents. But if the 

 rectus femoris has undergone, as I beheve, a similar modification of origin to that which 

 characterizes the tensor vagina, sartorius and biceps, it would, by its extension along the 

 spines of the sacrum, cover and mask the true glutceus externus, which arises from part 

 of the outer surface as well as from the crista of the ilium ; and by the same modification 

 of the rectus, that connection between the tensor and glutceus, which is present in some 

 quadrupeds, would be severed ; while the more common close proximity of origin of the 

 rectus and tensor is maintained. Already, in the Kangaroo, we find the origin of the 

 rectus femoris extending from above the acetabulum higher up than usual upon the iliac 

 bone. If, therefore, the great superficial muscle in question does not include the rectus 

 femoris with the tensor vagina, then, with the evidence of the true gluteus externus in 

 the muscle a PI. XXXII. of the Apteryx, I should feel bound to regard it as an enor- 

 mous development of the tensor vagina alone. 



Meckel assigns as his reason for regarding the muscle which I have called glutceus 

 externus to be the glutceus medius, that its origin and relations to the other levators and 

 abductors of the thigh are absolutely the same as the glutceus medius in Mammals'. It 

 is, he says, covered by the glutceus maximus, meaning h PI. XXXI., or the great ' pyra- 

 midal ' of Vicq. d'Azyr ; but we are not bound to admit, in the absence of proof, 

 that the great pyramidal of Vicq. d'Azyr is the glutceus maximus ; and until this be 

 satisfactorily established the argument is of no weight. Reasons have been already 

 given for regarding the glutceus externus of Meckel as the combined tensor vagince and 

 rectus femoris. The true glutceus externus is hidden in most birds, by the extraordinary 

 extension of the origin of the rectus extensor cruris on one side, and of the biceps flexor 

 cruris on the other ; but, though covered, the glutceus externus is the outermost of the 

 three glutei which are recognizable in the Apteryx. The more posterior position of 

 its origin and its lower insertion, together with its inferiority of size as compared with 

 the muscle which I have called glutceus medius, are characters which the glutceus externus 

 of the Apteryx has in common with that muscle in most Mammalia, and especially in 

 the genera Macropus and Dipus, which most resemble Struthious birds in the propor- 

 tions and functions of their locomotive extremities. 



To attempt to conceive the muscle PI. XXXII. a. to be the homologue of the pyrifor- 

 mis involves so anomalous an inversion of position in respect of the pelvis, of relations 

 to other muscles inserted into the proximal part of the femur, and of both origin and 

 insertion, as can only be accounted for by the difficulty in which Cuvier, having recog- 

 nized the true glutceus medius, found himself in respect to the homologue of the glutceus 

 externus, having applied the name of that muscle to the expanded tensor and rectus, by 

 which it is covered. 



' Loc. cit. p. 352. 



