ON CERTAIN MUSCLES OF BIRDS. 189 
the body, from which most of the feathers have been removed, should 
be laid on its side, and a section made in the skin, in a line parallel 
to and just over the femur, along its whole length; from the ex- 
tremities of this line the sections should be continued at right 
angles to it, extending upwards and downwards from the end over 
the head of the femur, and along the outer side of the leg from 
that at the knee. The skin must be then dissected downwards as a 
flap off the muscular adductor mass below, and some way upwards 
above the level of the femur. After this has been done the following 
muscles will be found without difficulty :-— 
Tensor fascie.—This is the superficial muscle of the outside of the Page 62” 
thigh, covering the femur. It is flat and triangular in shape, and 
arises as a membranous expansion which covers the gluteus ii, from 
the lower two-thirds of the posterior border of the iliac fossa in which 
that muscle is situated, and from the fibrous septum which separates 
that muscle from the gluteus iii. Further down it has origin also 
from the whole length of the ridge which separates the postacetabular 
area from the external lateral surface of the ischium, and which may 
be termed the postacetabular ridge, as well as from the posterior 
border of the ischium, as far forwards as its junction with the pubis, 
being here slightly overlapped by the semitendinosus. The fibres 
- converge towards the knee; and the deep portion of the muscle 
blends in its course with the vastus externus, together with which it 
continues forward to become part of the broad thin tendon which 
covers the knee and is inserted in the front of the tibia-head, the patella 
being situated in it, together with the long, slender, and flat tendon 
of the ambiens muscle, which is situated below it, running obliquely 
from inside and above, outwards and downwards. In many birds, as 
the Falconide and Psittaci, this muscle does not extend below the 
level of the femur, but ends inferiorly by blending with the vastus 
externus; and consequently, where such is the case, it evidently 
cannot, as it does otherwise, cover any of the flexors of the leg. In 
the Bucerotide it is entirely absent. Whether this postacetabular 
portion of the tensor fascis is present or absent has some bearing 
on classification, as in the different families it is a very constant 
feature. 
Biceps cruris——The anterior portion of this muscle may be seen in 
the Fowl’s leg before the tensor fascie has been removed, just below 
it, near its insertion. This muscle is mostly covered by the tensor 
fascie, arising from the upper three-fourths of the postacetabular 
ridge, just in front of the origin of that muscle. Its fibres converge 
to form a round tendon, which in the outer side of the popliteal 
region is bent sharply downwards by passing through a tendinous 
sling which arises from the lower end of the femur, to be inserted on a 
