Charles R. Bardeen 345 
nized, the peroneus anterior and peroneus posterior (Gadow, 82). The m. 
peroneus anterior extends in most forms from the proximal extremity of the 
fibula to the base of the fifth metatarsal. The peroneus posterior in croco- 
diles is more or less fused with the gastrocnemius and extends from the 
extensor musculature of the thigh to the calcaneus. In Hatteria and many 
saurians it is more or less fused with the peroneus anterior and extends 
from the lateral condyle of the femur to the outer side of the fifth metatarsal 
(Gadow, 82). In the mammals the peroneal group consists in most forms 
of three muscles, a peroneus longus, peroneus brevis, and peroneus 
extensorius. 
The peroneus longus may be inserted into the base of the fifth metatarsal 
or into various structures in the sole of the foot, as far as the base of the 
first metatarsal. In Ornithorhynchus the tendon of this muscle may be fol- 
lowed to this last insertion. 
The peroneus brevis and peroneus extensorius in Ornithorhynchus consti- 
tute a muscle, one part of which sends tendons to the extensor surface of 
the terminal phalanges of the first four toes, the other to that of the fifth 
toe. In marsupials the peroneus brevis is distinct from the peroneus ex- 
tensorius. The latter arises from the lateral condyle of the femur and from 
the fibula and sends tendons to the second and fifth toes. In rodents the 
peroneus extensorius sends tendons to the fourth and fifth toes. In carniv- 
ora it sends a tendon to the fifth toe. In some apes the peroneus exten- 
sorius is differentiated and sends a tendon to the fifth toe. In others it is 
not isolated from the peroneus brevis. In man a peroneus extensorius 
(peroneus quartus of Le Double) is not infrequently found as a variation 
under most diverse forms. Most frequently the tendon only is isolated and 
is inserted into the fifth metatarsal, cuboid, calcaneus, etc. The tendon of 
the peroneus brevis frequently sends expansions to the tendon of the fifth toe, 
that of the fourth toe, the metatarsal of the fourth toe, ete. In normal 
embryonic development, however, the peroneal musculature does not seem 
to become connected with the extensor tendon plate. 
b. Nerve Distribution. 
The nerves to the peroneal muscles probably arise from the more distal 
spinal nerves which go to form the peroneal nerve, but this cannot be 
satisfactorily determined by dissection. 
The nerves to the peroneal muscles (brevis and longus) may arise from 
the main trunk of the n. peroneus, from the n. peroneus superficialis, or 
from both. In 15 out of 20 instances a single branch passed from the 
n. peroneus superficialis to the peroneus brevis, in one instance two such 
nerves were given, in four instances the nerve arose from the more distal 
branch to the peroneus longus. 
In three instances out of 20 a single nerve branch ran from the n. 
peroneus to the peroneus longus muscle; in 8 instances two such branches. 
In four of these cases the second branch sent a nerve of supply to the 
