REPORT ON THE SPHENISCTD^. 107 



Nerve supply. — A branch from the obturator nerve. 



Variations. — In Pygosceles tcBniatus and Spheniscus detnersus this muscle is to some 

 extent separable into two distinct lamellae — an internal and an external. No trace of 

 this subdivision is observable in any other species. In Pygosceles, Eudyptes chrysolophus, 

 and Spheniscus magellanicus the posterior half of its muscular fibres terminates on the 

 tendon common to this muscle and to the inner head of origin of the gastrocnemius. 



Remarks. — Gervais and Alix speak of the adductores in Eudyptes c/irysoloj^hiis as 

 being attached to the ischium and pubis. Neither in this species nor in any other have 

 I been able to recognise more than a single adductor. In this connection it must be 

 remembered, that the muscle which I have named adductor longus constitutes a portion 

 of the femoro-coccygeus of these authors, and is not therefore regarded by them as consti- 

 tuting a second adductor. Meckel rightly observes that in the Penguin the posterior 

 fibres of the adductor magnus are united with the origin of the gastrocnemius, much in 

 the same way as are those of the semitendinosus in other birds. 



6. Obturator externus. 



Le muscle qui tient la place du quarre, Vicq d'Azyr, 1774, p. 49G, Xo. 10. 



Qaarre de la cuisse, Cuvier, vol. i. p. 355, No. 5. 



Der Schenkelr oiler, Wiedemann, p. 97. 



Der uussere HuftheMoch-Muskel, Tiedemann, p. 328, No. 5. 



Muscle No. 6, Meckel, vol. vi p. 84. 



Pi/ramidalis, Owen, p. 35. 



Quadratus femoris, Selenka, vol. vi. p. 140, No. 79. 



Le carre, Gervais and Alix, p. 32. 



Attachments. — The obturator externus arises from the whole of the outer surface 

 of the iscliium, behind the sciatic foramen, and below the origin of the biceps femoris. 

 The fibres pass horizontally forwards, to terminate on a stout tendon which is inserted 

 into a depression on the outer surface of the great trochanter of the femur, between the 

 insertions of the gluteus medius and gluteus minimus. 



Action. — The muscle rotates the femur outwards, and consequently directs the foot 

 inwards towards that of the o^jposite side. In this action the obturator externus is the 

 antagonist of the gluteus medius and minimus. 



Relations. — Superficially the muscle is concealed by the biceps and adductor longus, 

 and is crossed by the sciatic nerve. Its deeper surface rests upon the ischium. 



Nerve supply. — A branch from the obturator nerve. 



