64 
PRIMROSE : THE ANATOMY OF THE ORANG OUTANG 
the plantaris muscle. We find the muscle in a more fully developed 
condition in the lower mammalia. Cunningham^ described it in 
the marsupials. In Thylacinus this muscle arises in common with the 
outer head of the gastrocnemius and remains fused with its under 
surface for a considerable distance. It ends in a strong tendon which 
proceeds downwards along the inner side of the tendo Achillis to the 
heel, where it expands and, passing superficially to the tendo Achillis, 
enters the sole. Here it spreads out in the form of a plantar fascia which 
divides into three slips for the index, medius and annularis. The 
plantar fascia is not attached to the subjacent muscles, and each of its 
terminal slips bifurcates to embrace the metatarso-phalangeal joint and 
is attached to the ligamentous structures around that articulation. 
Sutton describes a somewhat similar arrangement in the Armadillo. 
In higher mammalia it would appear that, owing to the backward 
growth of the os calcis the plantaris is shut off from its direct connection 
with the plantar fascia, and terminates by being inserted into the os 
calcis itself 
The Flexor digitoruin fihularis (the flexor longus hallucis of human 
anatomy), was a very large bulky muscle of extensive origin from the 
posterior aspect of the external femoral condyle where it embraced the 
origin of the outer head of the gastrocnemius, also from the posterior 
and external lateral ligaments of the knee joint, the posterior aspect of 
the fibula as low as the junction between the middle and lower thirds, 
also from the fascia between it and the peronei muscles. 
The Flexor digitorum tibialis (the flexor longus digitorum of human 
anatomy), was also a very bulky muscle and arose from the posterior 
aspect of the tibia immediately external to the attachment of the 
popliteus muscle as high up as the head of the tibia ; it was attached 
along a line running downwards and inwards to the inner margin of the 
tibia at the junction of its upper and middle thirds. This portion of the 
muscle is joined by a well developed band of fibres descending from the 
fascia over the lower part of the popliteus muscle. These fibres may be 
traced upwards, and are found attached to the inner tuberosity of the 
tibia. Another very distinct head of origin of this muscle arose from 
the fascia over the tibialis posticus muscle, and extended as far as the 
inner margin of the fibula. 
The two muscles just described, viz., the flexor digitorum fibularis 
I D. J. Cunningham, “ Report on the Marsupialia, with an Account of the Comparative Anatomy 
of the intrinsic Muscles and Nerves of the Mammalian Pes.” Report of the Voyage of H. M. S. “ Chal- 
lenger,” Vol. V, 1882, Part XVI, p. 41. 
