246 MR. W. P. PYCRAFT ON THE MORPHOLOGY AND 
male &. darwini the ambiens of the left thigh stopped at the knee, as in the female, 
but in the right thigh the muscle was typically developed and passed the knee with a 
strong tendon. 
In Casuarius the ambiens, according to Garrod, is wanting. Concerning this, 
Dr. Gadow, in describing the ambiens of Rhea, a portion of which we have just 
quoted, continues, “ This abnormal condition of m. ambiens, which seems to be pre- 
vailing in Darwin’s Rhea, is the intermediate stage between a typically developed 
m. ambiens and such forms in which, as in Caswarius, this muscle has lost still more 
of its independence, and then only forms an additional head of the median part of 
the portio media m. femori tibialis s. vasti. Without an elaborate examination 
and comparison of the formation of these muscles with their nerve-supply, 
we should, with Garrod, come to the conclusion that Casuarius did not possess an 
ambiens muscle. The assumption of still further reduction of the distal portion of 
the m. ambiens explains what I have observed in some Passerine birds, ¢. g., in a 
specimen of Lanius bentet, in which the m. femori tibialis internus, besides being 
strongly developed, received in its proximal part a thin spindle-shaped semitendinous 
head from the pubic spine. This additional little slip is probably the last trace of 
the ambiens muscle, which is now generally lost by the Passerine birds. 
“The case above described is one way in which this muscle gets lost; in other cases, 
e. g., Ciconia and Phenicopterus, the reduction does not begin by its tendon becoming 
attached to the neighbouring tendons in the knee-region, but the whole muscle shows 
a diminution of its tendon and belly to a mere thread, till at last this also disappears, 
é. g., in Abdimia and Xenorhynchus.” 
The muscle-formule of the Palwognathe is as follows :— 
Strut hio 
iE I Care 
Casuarius 
Crypturi 
Rhea B.X.Y +. 
Dromeus B.X.Y—. 
The deep flexors of the foot of the Struthiones belong to the types IT. and IV. of 
Gadow. 
Apterya alone represents type II. ‘The vinculum is strong, and runs directly 
downward to join the flexor profundus. The flewor hallucis tendon is slender. 
Struthio, Rhea, Casaurius, and Dromeus all belong to type IV. The separate 
tendons of the flevor hallucis longus and of the fl. perforans s. profundus can 
be distinguished as far as the middle of the tarso-metatarse, when they completely 
fuse. 
flexor brevis digiti 111., which arises from the tendon of the flexor profundus and is 
inserted into digit 11., occurs only in Rhea amongst the Struthiones. 
