MYOLOGY OF OPISTHOCOMUS CRISTATUS. 563 
part of the middle third. It is inserted into the base of the great trochanter, its external 
surface, below the medius and above the origin of the vastus externus. 
The gluteus quartus is a small muscle arising from the prominent process of bone 
which springs from the posterior acetabular border. It is inserted into the great tro- 
chanter of the femur, behind the medius and on the same plane. This muscle resembles 
rather the gemellus superior than a fourth gluteus, especially as its position is imme- 
diately above the obturator internus. 
There is a somewhat peculiar muscle, which I am inclined to think is the semimem- 
branosus. It arises from the shelving process of the ischium, and from the surface of 
bone below and behind it, by muscular fibres. It increases in size as it passes down- 
wards and forwards, and is inserted into the lower end of the femur, behind the outer 
head of the gastrocnemius and the bicipital loop. A few of its fibres extend as low 
down as the posterior surface of the upper extremity of the tibia. The great sciatic 
nerve lies superficial to it. 
The femoro-caudal muscle is connected by a small band of muscular fibres with the 
preceding muscle. 
The obturators, adductors, and quadratus femoris are present and well developed, but 
‘present no special peculiarities. 
The psoas, iliacus, and pectineus are rudimentary. 
The great sciatic nerve is divided into peroneal and popliteal from its exit through 
the ischiatic foramen. They lie parallel, and are enveloped in the same sheath. About 
_ the middle of the thigh there is an intercommunicating branch. In the common 
Pigeon &c. this division only takes place, as in Man, opposite the lower third of the 
thigh. Probably it is accidental, or if not, is present occasionally in different specimens 
of the same species of birds. 
The external popliteal (peroneal) nerve passes through the bicipital loop with tendon 
of biceps. This is constant in birds. 
The peronwus longus is a broad and expanded muscle at its origin. It arises by an 
aponeurosis from the mesial tubercle of the tibia, which conceals the upper half of the 
tibialis anticus muscle. It springs also by fleshy fibres from the whole length of the 
rudimentary fibula, and it receives a few additional fibres from the tibia. The tendon 
resulting from its fleshy belly divides opposite the lower third of the tibia into two 
portions, an anterior and a posterior. The anterior tendon terminates on the dorsal 
aspect of the foot ina broad expansion, which is inserted into the base of the first 
phalanx of the external digit. The posterior tendon follows the usual course. 
The peroneal nerve has the same relation to this muscle as in the higher animals. 
The peroneus brevis arises from the remainder true portion of the fibula, also from 
the lower two thirds of the shaft of the tibia. It is inserted by a short tendon into the 
base of the outer metatarsal bone. 
Lhe tibialis anticus (P). LXV.) is a large fleshy muscle. Its origin is average. It is 
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