ON CERTAIN MUSCLES OF BIRDS. 205 
The Pygopodes consist of two distinct families. 
Among the Oolymbide, Colymbus glacialis possesses the ambiens, 
the femoro-caudal, the accessory femoro-caudal, the semitendinosus, 
and the postacetabular portion of the tensor fascise; the accessory 
semitendinosus is absent. 
The Podicipide possess the accessory femoro-caudal, the semiten- 
dinosus, and the postacetabular portion of the tensor fascie; the 
ambiens, the femoro-caudal, and the accessory semitendinosus are 
absent. In these birds the semimembranosus is very thin in Podiceps 
minor; in specimens preserved in spirit I have not seen it, probably 
because it is so slender. 
Species examined. 
Podiceps cristatus. Podiceps nove-hollandie. 
— minor. 
The Alcide possess the femoro-caudal, the accessory femoro- 
caudal, the semitendinosus, and the postacetabular portion of the 
tensor fascie; the ambiens and the accessory semitendinosus are 
absent. 
Species examined. 
Alca torda. Arctica alle. 
Uria troile. 
The Impennes possess the ambiens, the femoro-caudal, the acces- 
sory femoro-caudal, and the semitendinosus; the accessory semiten- 
dinosus and the postacetabular portion of the tensor fasciz are absent. 
In Eudyptes the insertion of the femoro-candal is much nearer the 
condyloid end of the femur than to the head. 
Species examined. 
Aptenodytes pennantit. Spheniscus humboldti. 
Spheniscus demersus. Eudyptes catarractes. 
The Crypturi possess the ambiens, the femoro-caudal, the acces- 
sory femoro-caudal (which has a slip arising above the sciatic foramen, 
found elsewhere only in the Struthiones), the semitendinosus, the 
accessory semitendinosus, and the postacetabular portion of the tensor 
fasciz. 
Species examined. 
Rhynchotus rufescens. Crypturus sallei. 
Crypturus obsoletus. noctivagus. 
The Struthiones present marked peculiarities. Page 643. 
In Apteryz the postacetabular portion of the tensor fascie is very — 
large, and slightly overlapped at the lowest point of its origin by the 
