484 DR. R. W. SHUFELDT ON [Nov. 16, 
It will at once be seen that Geococcyx. californianus, in common 
with the vast majority of birds, has no special tendon devoted to the 
flexing of the second or prebasal phalanx of the fourth toe (here the 
reversed one). Provision is made for this in various ways in different 
birds. Here, in the subject before us, a special slip is thrown off 
for attachment from the deep flexor tendon as it passes over the 
prebasal joint in question, which slip virtually fulfils the function 
of a flexor perforatus annularis secundus pedis, did such a muscle 
with an independent tendon exist. 
The flexor perforans digitorum profundus (Plate XLV. fig. 2, 
S-p-p). This muscle is deep to all the flexors, and is situated directly 
on the posterior aspect of the tibia and fibula. It arises by two 
heads, one from the upper part of the tibia immediately below the 
overhanging rim of its summit, and the other, smaller, from the back 
of the head of the fibula. In the Corvide there is a well-developed 
third head, which comes off from above the fibular notch of the outer 
condyle of the femur, and in these birds, too, there is no fibular head 
to this muscle, but two tibial ones instead. Geococcyx agrees 
however, with most birds in having this muscle attached nearly the 
whole length of the posterior aspect of the shaft of the tibia by lightly 
attached carneous fibres. 
About a centimetre about the tibial cartilage it terminates in a 
strong subcompressed tendon, which, passing beneath the cartilage 
referred to, crosses the ankle-joint in front of all the other flexor 
tendons, and then passes through the inner of the two longitudinal 
perforations of the hypotarsal apophysis of the tarso-metatarsus. 
Down the posterior aspect of the shaft of this bone the tendon still 
maintains its anterior position and exhibits a predisposition to 
ossify. But this does not actually take place in the specimen before 
me. Above the distal trochlee, it makes the fibrous connection 
with the tendon of the flexor longus hallucis already described. 
This band is shown in the figure. Once within the limits of the post- 
trochlear space, the tendon of this muscle behaves in a manner 
common to most birds—that is, it quadrifureates, and each branch 
takes a course close up to the joints on their plantar aspects, and 
running through the slits in the perforated tendons pass in each 
case to the ends of the toes, where they become attached or in- 
serted upon the infero-proximal tubercles of the unequal phalanges. 
The one passing along under the fourth digit sends up a slip which 
is attached to the underside of the shaft of the prebasal joint, thus 
making good the deficiency here of what is represented in the other 
toes by an independent tendon. 
The tibial head of this muscle at its origin is directly covered by 
the soleus, while in the aperture existing between the two heads we 
can discern the popliteus. 
These flexor muscles, and others on both the front and rear of 
this limb, are moulded upon each other in a manner that can only be 
justly appreciated by a personal examination. In some the con- 
nections are quite feeble, the intervening tissue being easily separable, 
while in others the intimacy is very close, and great care is 
