528 Proceedings of the Royal Irish Academy, 
the tibia and fibula is attached very far forwards, so that the muscles 
of the back of the leg occupy the inner aspects of both bones. 
Gastrocnemius (externus '09 ; internus -11) arises by two heads, 
one from each condyle of the femur ; they are perfectly separate for 
their entire muscular part (which is longer in externus than in internus) ; 
the insertion is by a single tendon into the calcaneum. The action of 
the whole of this muscle is to invert the sole of the foot. 
Soleus ("08) arises from the middle third (upper fourth, Professor 
Macalister; upper two- thirds, Professor Humphry) of the back of the 
fibula, with a tendinous slip extending to the head of that bone (Arcto- 
pithecus), and has a fleshy insertion into the inner side of the back of 
the calcaneum underneath gastrocnemius. There are no fabellte in the 
origins of either this or the last muscle. 
Popliteus (•08) takes origin from the external condyle of the femur, 
and is inserted into the upper third of the back of the tibia. There is 
a large wedge-shaped fabella in the origin of this muscle, the tibial 
surface of which is the larger, and articulates both with the femur 
and tibia. 
Plantaris ('24) large and elongated, arises above the head -of gastro- 
cnemius externus, and is inserted into that part of the tendon of flexor 
digitorum longus, which supplies the middle and outer digits. Pro- 
fessor Humphry did not find this muscle distinct in the animal he 
dissected, but considers the femoral origin of flexor digitorum to 
represent it. 
Elexor digitorum longus (slip to inner toe "16 ; to middle "I I ; to 
outer '25) is an enormous muscle, with the parts which supply the ten- 
dons to the inner and middle toes arising from the posterior aspect of the 
tibia, and that for the outer toe by two heads, one small from the 
middle of the tibia, and one large from the upper four-fifths of the 
fibula and from the strong external lateral ligament of the knee ; it 
receives the plantaris tendon as above described, and is inserted as usual. 
The bicipital tibio-fibular originis not described by Professor Macalister, 
whilst Professor Humphry found it arising in three parts, one from 
the external condyle of the femur (plantaris), another (the smallest) 
from the tibia, and a third from the back of the fibula ; these supply 
respectively the tendons to the middle, inner, and outer digits. 
Plexor hallucis longus arises from the fibula and interosseus mem- 
brane, and uniting with the last muscle is inserted into all three 
digits. 
Tibialis posticus ('04) arises from the lower half of the back of the 
tibia (and from the head of the fibula in Arctopithecus), and is inserted 
into the ento cuneiform. 
Plexor brevis is described by Professor Humphry as a small muscle 
arising from the calcaneum, and inserted into the sheath of flexor 
digitorum. We could not find it in our specimen, but it may have been 
removed in skinning. 
Accessorius (inner slip '05 ; middle '03 ; outer point, '12 ;) double, 
one part arising from the outer surface of the os calcis, is inserted into 
