Page 341, 
290 ON THE DEEP PLANTAR TENDONS IN BIRDS. 
themselves peculiarities as important as that which so definitely 
characterizes the Passeres. To describe and to endeavour to show the 
bearing of these differences are the objects of the present paper. 
In birds generally, whatever the number of their toes, there are 
two muscles whose fleshy bellies are situated in the leg proper (that 
is, between the knee and the ankle), deep, and just behind the tibia. 
These muscles arise, one from almost the whole of the posterior sur- 
face of the tibia and from the fibula, in a bipenniform manner, and 
the other from the inferior surface of the horizontal femur, just be- 
hind the outer genual articular condyle. The former is termed the 
flexor perforans digitorum pedis, because its terminal tendons per- 
forate those of the more superficial flexors on their way to the ungual 
phalanges of their respective toes; and the latter is termed the flewor 
longus hallucis, because there is generally a shorter muscle to the same 
digit. 
These two muscles descend to the ankle (the joint between the 
tibio-tarsus and the tarso-metatarsus) side by side; they run behind 
it, in the fibro-cartilaginous or osseous mass which, in birds, is always 
found at the posterior part of the upper end of the tarso-metatarse, 
in two canals, deeper than any of the other flexor tendons; and in 
these canals there is always a definite relation between them. Some- 
times the tendons are side by side; and then it is always that of the 
flewor longus hallucis which is the external of the two, the osseous 
vertical ridge, which is nearly always seen in the dry bone, separating 
them. Sometimes, however, one is superficial or, in other words, 
posterior to the other. When this is the case it is always the flexor 
perforans digitorum which is the deeper. In the Swifts, for instance, 
the flecor longus hallucis quite covers the flexor perforans digitorum ; 
but in most Parrots, as may be seen by the disposition of the osseous 
canals in the dry tarso-metatarse, that for the former muscle is exter- 
nal as well as superficial, only partially covering it. 
These relations are constant, and must be always borne in mind 
in all attempts to identify the muscles. From these it can be inferred, 
as is verified by dissection, that the tendon of the flewor longus hallucis 
crosses its companion superficially on its way from the ankle to its 
insertion in the hallux. 
Just before, or just at the commencement of, the sole of the bird’s 
foot (near the joint between the metatarsus and the phalanges), these 
two tendons generally split up to supply the toes. By far the majority 
of the families of birds agree in the distribution of the terminal 
tendons, conforming to one common type. This typical arrangement 
must be first described. The common Fowl (Gallus bankiva) is a very 
good example. The accompanying diagram (fig. 1) will assist in 
explaining it. The tendon of the flezor longus hallucis descending on 
