282 ZAGLOSSUS. 



Next internal to the muscle last described arises what is doubtless the 

 extensor longus digitorum (Plate 1, fig. 1, e^- Its origin is from a flat broad 

 tendon from the outer epicondyle of the femur, between the ascending process 

 of the fibula and the patella. It passes to the inner tubercle of the fibula on 

 which it is inserted and thence into a large flattish muscle that arises from the 

 proximal half or more of the fibula, and (medially) from the interosseous fibers 

 between tibia and fibula. This muscle is easily divisible into three parts: — the 

 most external comes off superficially from the main muscular mass at 20 mm. 

 below the head of the fibula and continues as a small spindle-shaped muscle to 

 the distal head of the fibula where it passes into a delicate tendon that inserts 

 as a thin sheet at the base of the fifth digit. In the Echidna Mivart found 

 this branch insertmg on the fourth digit of the left leg, but on the fifth digit of 

 the right leg. He considers it a part of the /e.ror longus digitorum. Westling 

 also in the Echidna, found a similar branch, whose tendon, however, became 

 divided into two, the outer to the fifth, the inner to the fourth digit. This 

 author considers the outer branch the equivalent of the peroneus brevis, and names 

 the muscle extensor digitorum IV et V. From the condition in the Proechidna, 

 however, it seems better to consider this muscle as representing a branch to 

 the fifth digit from the extensor longus digitorum that, on acount of the reduction 

 of the fifth digit, is in process of becoming quite separated. The branch to the 

 fourth digit noted by Westling may be due to an imperfect separation of the 

 fourth digit's tendon, since the small muscle is very closely appressed against 

 the edge of the extensor longus. 



The main portion of the extensor longus is radially compressed, but becomes 

 flattened as it passes through the groove between the distal heads of tibia and 

 fibula. On the tarsus it spreads out as a thin sheet of fascia to the bases of 

 digits 2, 3, and 4. This sheet is continuous at the bases of the phalanges with 

 the tendon to the fifth digit above noted. 



Closely approxmiated against the medial border of this main portion, is 

 another muscle nearly as large proximally, but passing at the distal epiphysis 

 into a broad flat tendon. At the metatarsals this tendon becomes dorsal to 

 that of the main tendon of the longus digitorum and goes to the bases of the 

 second (mainly) and third phalanges. In the Echidna, the same condition was 

 found by Westling, who names the muscle extensor digili II. Mivart noted only 

 the main insertion, that on the second digit, and considers the muscle 

 equivalent to the extensor longus hallucis, even though it has no connection with 

 the hallux. It is possibly a derivative of the extensor longus digitorum. 



