378 
On the Sesamoids of the Knee- Joint 
Macalister* pojMtens in birds may be femoro-tibial or fibulo-tibial in origin, and 
the origin of soleus is also variable. There is of course the possibility that jiopliteus 
was not in the earlier stage largely fibular in its attachment, but acquired an 
attachment to the fibula in the marsupials. This appears to be the view of Parsons 
who writes f : 
In the koaliis, the phalanger, the opossum and the Tasmanian devil, the great mobihty of the 
fibula has produced the same effect on the poplitexis that we noticed in the lemur, the fleshy 
part acquires an attachment to the fibula, while the tendon is converted into an extra external 
lateral ligament. 
The question arises, however, as to whether the popliteal attachment to the 
fibula is not the earlier stage and thus the arrangement we find in the lemur would 
be vestigial. When the parafibula broke up, it is conceivable that popliteus carried 
off with the cyamella the whole or a portion of a fibulo-femoral ligament, i.e. it is 
not the tendon of popliteus converted into a ligament, but a ligament which has 
become the tendon of popliteus. 
The point has been studied also by Gordon Taylor and W. V. BonneyJ. They 
take the view that the ultimate origin of the popliteus was fibular ; that as move- 
ment between the tibia and fibula cea.sed to exist the upper origin of popliteus 
ascended to the external femoral condyles, but that in the lemur where movement 
between tibia and fibula has reappeared the popliteus appears to be descending to its 
primitive fibular attachment. The lemur problem is a question either of reversion 
or of vestige. The question of whether the fibula attachment of popliteus is the 
original attachment or an acquired one seems worthy of much more study especially 
in relation to the origin of the lateral knee-joint sesamoids, in particular to the 
muscular attachments of the parafibula in Reptiles. 
Passing from the Monotremes to the Marsupials it becomes difficult to appreciate 
the contributions of various writers to the subject, for they invariably speak of the 
paratibular sesamoid as if it were a large fabella in the lateral head of gastrocnemius. 
Thus we find it hard to interpret the following statement of Macalister with 
regard to the myology of the Marsupials§ : 
The gastrocnemius e.vtcnms in the Wombat, Giant Kangaroo, Sarcophilus and Bennett's 
Kangaroo arises from the .sesamoid-bone at the back of the external condjde of the femur and is 
inserted into the tendo Achilles, etc. 
It seems to us extremely difficult to speak of the parafibular sesamoid, which 
may even be fused to the fibular head, in the Wombat and Tasmanian Devil (see 
our Plate XXIX, Fig. 78) as a sesamoid at the back of the external condyle ! The 
same difficulty occurs in the Wallaby (Bennett's kangaroo, or Halmaturus): see 
* " On some Points in Bird Myology," Proc. R. Irish Academy, Vol. ii. 1875—77, p. 57. 
t " Joints of Mammals compared with those of Man," Journal of Anatomy and Physiology , Vol. xxxiv. 
p. 313, 1900. 
X " Homology and Morphology of Popliteus," Journal of Anatomy and Physiology, Vol. xxxix. p. 35. 
§ " Myology of the Wombat {Phascolomys womhata) and the Tasmanian Devil {Sarcophilus wsinus)," 
Annals of Natural History, 1870, p. 19 of our offprint. 
