Karl Pearson and Adelaide G. Davin 
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whole of the popliteal surface, while the external gastrocnemius originates from the parafibular sesamoid. 
The drawing is also intended to show the tendinous fibres running from gastrocnemius externus to the 
lateral border of the patella ; a few, cut through in drawing in order to expose the patella, run to the 
lateral face of the external condyle. The popliteal tendon can also be seen taking origin in the popliteal 
groove of the external condyle. It passes across the head of the fibula, its internal border being con- 
nected with the external semilunar cartilage, while the external fibres run down to the muscle fibres of 
the popliteus. This latter arises from the upper third of the posterior surface of the fibula. The 
double nature of gastrocnemius externus suggests that the deeper portion is soleus, although Macalister 
("Myology of the Wombat and the Tasmanian Devil," Annals of Natural History, 1870, p. 19 (offprint)) 
suggests that soleus has a fibular origin. 
Plate XJ^XII, Fig. 82 a and Fig. 82 h. Drawings of the posterior aspect of the left pelvic limb 
of Phascolarctus cinereus, the Koala, with the muscles attached. Fig. 82 a shows the popliteal muscle 
and the external gastrocnemius with the parafibular sesamoid covered by its fibres. Fig. 82 6 shows 
gastrocnemius cut and turned back, so that the facet of the sesamoid which articulates with the fibula 
is exhibited and the position on which it rests on the fibular head is seen. This sketch is also intended to 
illustrate the following relations. The fleshy portion of popliteus is attached to fibula, and popliteal 
tendon runs from the anterior proximal corner of fibula to popliteal groove on external condyle. Also 
tendinous fibres from the fleshy portion on fibula cross the posterior surface of the latter and mingle 
with the tendinous fibres of gastrocnemius which run from the sesamoid to the external condyle. (See 
also Fig. 86.) 
Plate XXXIII, Fig. 83 n and Fig. 83 6. Macropus sp. The portion of the knee-joint of a kangaroo 
(species ?) here drawn was most kindly sent to us by Dr W. C. Mackenzie of the Australian Institute of 
Anatomical Research. It consists only of the lateral branch of gastrocnemius with its sesamoid and the 
cyamella, together with the external semilunar cartilage attached. It was thus not possible to draw 
these in their natural position. It should not be impossible, however, to understand the relations to 
other structures if the reader will compare these drawings with those of other Marsupialia. The three 
important components are the externaA fabella, the cartilaginous cyamella, with surface which articulates 
with the fibular head, and the externaf semilunar cartilage. These are drawn in two aspects, the 
interesting point being that in the kangaroo the lower part of tlie parafibula, still articulating with 
the fibular head on the distal face and with the external fabella on the proximal has become purely 
cartilaginous. 
Fig. 84. Drawing of the posterior aspect of the left knee-joint of Didelphys virginiana, the Virginian 
Opossum. Here a is the popliteal tendon from groove on external condyle, 6 is the cyamella in the 
popliteal tendon as it passes over fibular head, c and d are branches of popliteal muscle running from 
tendon attached to cyamella, e is the external fabella in tendon of gastrocnemius, g and g' are the cut 
ends of gastrocnemius. The gastrocnemius has been cut just below its insertion on top of the external 
condyle to enable it to be pulled aside and display the fabella. When the leg is fully flexed the external 
fabella lies on the external condyle, and the cyamella is in direct contact with the lower surface of the 
condyle and the fabella. 
Fig. 85. Drawing of the lateral aspect of the left knee-joint of Phalangista vulpina, the Wolflne 
Phalanger. a is the parafibular sesamoid resting on the head of the fibula, 6 is the popliteal tendon. If 
the reader will compare this drawing with Fig. 78, he will grasp how parafibula and fibula united give 
a single complete bone. It is not possible to term the sesamoid of Phalangista merely a, fabella. 
Fig. 86. A further drawing of the posterior aspect of the right knee-joint of Phascolarctus cinereus 
after removal of the muscles, a is the tendon of gastrocnemius externus attached to femur above external 
condyle, b is the cut end of gastrocnemius e.ttermis, c is the fibular "collateral" ligament, d is the 
popliteal tendon running to head of fibula, the lower portion of popliteal tendon has been removed. 
From a specimen kindly sent by Dr W. Colin Mackenzie. 
Plate XXXIV, Fig. 87. Femur of Macropus bennettii, the Wallaby, with parafibular sesamoid attached 
above the external condyle. 
Fig. 88. Perameles lagotis, the Rabbit-eared Perameles, with parafibular sesamoid attached above the 
external condyle. 
Figs. 87 and 88 are photographs of museum specimens and we hold that they place the sesamoid in an 
erroneous position, leading it to be confused with a lateral /a6eita. 
