MR. ST. G. MIVART ON THE ANATOMY OF ECHIDNA HYSTRIX. . 893 
rise to a strong tendon, which passes down in a groove (lined with synovial membrane) 
on the anterior aspect of the tibial side of the lower part of the tibia and of the internal 
malleolus, and, passing beneath the tendon of the second part of the £ibialis anticus, it is 
inserted into the dorsal surface of the entocuneiform. 
The second and more external (Plate LIII. figs. 2 & 3, T.4 2) muscle is of about the 
same size as the preceding; it arises from the upper three-fifths of the anterior surface 
of the tibia, its fibres taking origin lower down than those of the first part; and its 
tendon passes in a marked groove (lined with synovial membrane) immediately external 
to the groove of the muscle last described, but quite distinct from it. It then crosses 
over the tendon of that muscle and is inserted into the dorsum of the proximal phalanx 
of the hallux, but gives off a small slip, which passes forwards and outwards and joins 
the tendon of the extensor longus hallueis. 
Meckel’ speaks of this muscle having two distinct heads in the Ornithorhynchus. 
. The extensor longus hallucis (Plate LIII. figs. 2 & 3, z.L.u), largely developed, though 
somewhat laterally compressed, arises from the upper half of the tibial border of the 
ulna and from the interosseous membrane. Its tendon passes down in a groove on the 
anterior surface of the bone, and is inserted into the last phalanx of the index of the 
foot towards its inner or tibial side. 
In the Ornithorhynchus? this muscle is inserted into the hallux. 
Extensor digitorum longus (Plate LIII. figs. 2 & 3, E.1.D).—This large muscle seems 
to be separable into two or perhaps three more or less distinct portions. It arises from 
the head of the fibula (slightly in front of, but principally behind, the lower attachment 
of the external lateral ligament), from the upper two-fifths of the tibial border of the 
fibula, from the intermuscular septa, and, very slightly, from the interosseous membrane. 
The main portion gives rise to a strong tendon, which divides into three, and is inserted 
into the second, third, and fourth digits. 
À small and more or less distinct portion, on the peroneal side of the main part of the 
muscle, gives origin to a long and delicate tendon, which is inserted into the dorsum of 
the fourth digit. ; ti 
In the right leg a third, also small portion, placed close beside the last, gives origin to 
à very delicate tendon, which is inserted into the fifth digit. 
There appears to be a considerable difference between the Echidna andOrnithorhynchus* 
in the arrangement of the extensor muscles and tendons. 
Extensor brevis digitorum.—1 could find no trace of this muscle. | 
The peroneus longus (Plate LIII. fig.3, .1) is a large muscle, and arises from the anterior 
Surface of the upper half of the fibula, including its singularly produced upper extremity. 
At about the commencement of the lowest fifth of the fibula it gives origin to a strong 
tendon, which descends and passes obliquely inwards (towards the tibia), and then dips 
down between the curiously reflected calcaneum and the peroneal border of the cuboid, 
and, running along a groove in the plantar surface of that bone, and crossing the sole of 
the foot, is inserted into the plantar surface of the proximal phalanx of the hallux. 
The peronœus brevis and peroneus tertius are both wanting. 
* Loc. cit, p. 29. * Meckel, l. c. p. 29, & tab. v. f. 38. 3 Meckel, loc. cit. p. 29, & tab. v. 
