394 MR. ST. G. MIVART ON THE ANATOMY OF ECHIDNA HYSTRIX. 
Gastrocnemius (Plate LITI. fig. 1, 6.0), —This is a delicate and slender muscle, which 
has a single but broad origin extending obliquely upwards and inwards from the in- 
ternal condyle of the femur. Rather below the middle of the leg it gives origin to a 
moderately strong tendon, which is inserted into the peroneal side of the os calcis. 
Soleus (Plate LIII. fig. 1, s.0).—A muscle somewhat smaller than the gastrocnemius, 
and which I take to be the soleus, arises, by tendinous fibres, from the posterior and outer 
margin of the singular process at the summit of the fibula, but not at all from the tibia. 
In the middle of the leg it gives origin to a tendon (of about the same size as that of the 
gastrocnemius), which is inserted into the os caleis rather on its tibial side, therefore 
crossing over beneath the tendon of the muscle last described. 
This muscle and the preceding one differ considerably from their homologues in the 
Ornithorhynchus '. 
The plantaris (Plate LIII. fig. 1, PLA) arises from the extremity of the posterior or 
inner surface of the process at the summit of the fibula, and about the middle of the leg 
gives origin to a tendon of nearly the same size as that of the soleus. This passes 
obliquely downwards towards the tibia and along a groove on the inner surface of the 
lower end of that bone, and is inserted into the plantar fascia. 
The popliteus also arises from the extremity of the process at the summit of the fibula, 
instead of from the external condyle. Its fibres pass obliquely downwards and inwards, 
and are inserted into the posterior surface of the tibia. The muscle extends, as a very 
thin layer, a long way down on the back of the interosseous membrane. 
Tibialis posticus (Plate LIII. fig. 1, v.P).—This is a very large and strong muscle. It 
arises from the whole posterior surface of the fibula, almost down to the ankle-joint, and 
gives origin to an extremely strong tendon, which is inserted into the plantar surface of 
the astragalus at its junction with the naviculare. 
Flexor longus digitorum (Plate LIII. fig. 1, r.1.D).—A muscle about as large as the 
preceding. It arises from the upper two-thirds of the posterior and external (peroneal) 
surface of the fibula, between the origin of the peroneus longus and the tibialis posticus. 
Just above the distal end of the tibia it gives origin to a very strong tendon, which 
passes in a groove between the os calcis and astragalus, and then divides into five 
tendons, which are respectively inserted into the last phalanx of each of the five digits. 
There seems to be no flexor longus hallucis or flexor brevis digitorum. 
Some muscular fibres appear to arise from the plantar surface of the recurved 0s calcis, 
and to be inserted into the outer side of the tendon of the long flexor of the digits. They 
may possibly represent the flexor accessorius. 
Other muscular fibres also arise from the os calcis, and are inserted into the metatarsal 
bone and proximal phalanx of the fifth digit. : 
a enter muscles are present in the posterior extremity as well i 
"eim or one, taking origin from the deep plantar fascia; but they are destitute © 
distinet delicate tendons which characterize the interossei of the hand, and have merely 
an aponeurotic insertion into their respective digits. 
* Meckel, J. c, p.29; Owen, l c. p. 382. 
