_+Musculus peroneus brevis+_ (Figs. 2, 3).--Lying along the anterolateral surface of the tibia, this slender, pinnate muscle arises from a fleshy origin along this surface and along the anterior surface of the fibula from a point immediately proximal to the insertion of the _m. biceps femoris_ to a point approximately two-thirds of the way down the crus. Near the distal end of the tibia the muscle gives rise to the tendon of insertion that passes through a groove on the anterolateral edge of the tibia just above the external condyle. Here the tendon is held in place by a broad fibrous loop and passes under the anterior branch of the tendon of insertion of the _m. peroneus longus_ and inserts on a prominence on the lateral edge of the proximal end of the tarsometatarsus. Action.--Extends tarsometatarsus and may abduct it slightly. Comparison.--No significant differences noted among the species studied. _+Musculus gastrocnemius+_ (Figs. 1, 4).--The largest muscle of the pelvic appendage, it covers superficially all of the posterior surface, most of the medial surface, and half of the lateral surface of the crus. The muscle originates by three distinct heads. The _pars externa_ covers the posterolateral surface of the crus, is intermediate in size between the other two heads, and arises by a short, strong tendon from a small bony protuberance on the posterolateral side of the distal end of the femur immediately proximal to the fibular condyle. The tendon is intimately connected with the distal arm of the loop for the _m. biceps femoris_. The _pars media_ is the smallest of the three heads and lies on the medial surface of the crus. The head of the _pars media_ is separated from the _pars interna_ by the tendon of insertion of the _m. semimembranosus_ and originates by a short, strong tendon from the posteromedial surface of the proximal end of the internal condyle of the femur. The proximal portion of the _pars media_ has tendinous connections with the tendon of the _m. semitendinosus_ and with the _pars posticus_ of the _m. adductor longus et brevis_. The _pars interna_ is the largest of the three heads and covers most of the medial surface of the crus. This head in its proximal portion is distinctly divided into anterior and posterior parts, the former overlapping the latter medially. The origin of the posterior part is fleshy from the anterior half of the tibial head. Some of the fibers of the anterior part arise directly from the inner cnemial crest while its remaining fibers arise from the patellar tendon (Fig. 1) and form a band that extends around the anterior surface of the knee, covering the insertion of the _m. sartorius_.