1873.] CERTAIN MUSCLES OF BIRDS. 637 



tenms of these birds, which is perplexing at first sight. In Sula 

 this muscle, instead of, as usual, being inserted into the outside of 

 the head of the femur, has its attachment further forward, to the 

 outer edge of the linea aspera, or the bony surface corresponding to 

 it, midway between the head of the bone and the attachment of the 

 femoro-caudal muscle. In Phalacrocorax it is situated still further 

 forward, being in contact by its anterior border with the posterior 

 margin of the femoro-caudal, parallel to it in direction, and otherwise 

 in situation exactly like an accessory femoro-caudal. However, that 

 it is the obturator externus and not the accessory femoro-caudal is 

 certain, from the facts that the nerve to the semimembranosus is 

 superficial to it, that the whole upper part of its outer surface is 

 covered with a tendinous layer, that none of its anterior fibres blend 

 with the posterior margin of the upper end of the tendon of the 

 femoro-caudal, and that the presence of this muscle is constant in 

 birds. The accessory femoro-caudal is, on the contrary, superficial 

 to the nerve to the semimembranosus ; it is not tendinous externally 

 up to its insertion ; some of its fibres blend with the tendon of the 

 femoro-caudal just before it joins the femur ; and its presence is un- 

 certain. In Sula the ambiens has a tendinous link at the outer side 

 of the knee, which runs upwards from it to the outer side of the 

 anterior fibrous expansion over the joint. 



Species examined. 

 Sula bassana. Phalacrocorax lugubris. 



Phalacrocorax carbo. 



The Ardeidce possess the femoro-caudal, though in some, as Ardea 

 goliath, it is extremely narrow, the semitendinosus, the accessory 

 semitendinosus, and the postacetabular portion of the tensor fasciae 

 which is very slightly developed ; the ambiens and the accessory 

 femoro-caudal are absent. 



Species examined. 

 Ardea cinerea. Ardea egretta. 



goliath. garzetta. 



purpurea. Nycticorax europceus. 



alba. Botaurus stellaris. 



The Ciconiidce possess the ambiens, the semitendinosus, and the 

 accessory semitendinosus ; the accessory femoro-caudal is absent. 

 The femoro-caudal is very small in Ciconia and absent in Leptoptilus ; 

 and the postacetabular portion of the tensor fasciae is the same. 



Species examined. 

 Ciconia alba. Ciconia maguari. 

 nigra. Leptoptilus crumeniferus. 



The Plataleidce possess the ambiens, the femoro-caudal, the 

 accessory femoro-caudal, the semitendinosus, the accessory semiten- 

 dinosus, and the postacetabular portion of the tensor fasciae, which 

 is small. 



