282 ZAGLOSSUS. 
Next internal to the muscle last described arises what is doubtless the 
extensor longus digitorum (Plate 1, fig. 1, el). 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 inserting on the fourth digit of the left leg, but on the fifth digit of 
the right leg. He considers it a part of the flexor 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 digitorwm 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 approximated 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 digiti IT. 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. 
