Page 636. 
Page 637. 
198 ON CERTAIN MUSCLES OF BIRDS. 
Bubo capensis. Athene passerina. 
poénsis. brama. 
fasciolatus. Pholeoptyna cwnicularia. 
Ketupa javanica. Glaucidium, sp. 
Scops zorca. Pulsatria torquata. 
Athene noctua. Surnia funerea. 
The Steganopodes must be considered in separate families. I have 
not dissected Pelecanus. 
Fregata aquila possesses the ambiens and the femoro-caudal, the 
latter being very slender; the accessory femoro-caudal, the semiten- 
dinosus, the accessory semitendinosus, and the postacetabular portion 
of the tensor fasciz are absent, 
Phaethon possesses the femoro-caudal (small), the semitendinosus 
(strong), and the accessory semitendinosus; the ambiens, the accessory 
femoro-caudal, and the postacetabular portion of the tensor fascie are 
absent. In this bird the biceps cruris is inserted into the fibula-head 
directly, without passing through a loop. 
‘The family Phalacrocoracide possess the ambiens,* the femoro- 
caudal, and the semitendinosus; the accessory femoro-caudal, the 
accessory semitendinosus, and the postacetabular portion of the tensor 
fascie are absent. There is a peculiarity about the obturator externus 
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 Phalacrocoraz 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 uncertain. In Sula the ambiens has a tendinous link at the outer 
* Meckel did not find the ambiens in the Cormorant; it is peculiar in that it 
runs through the substance of the large triangular patella, in a bon} canal. 
