374 
On the Sesamoids of the Knee- Joint 
But a preparation in the Museum of the Royal College of Surgeons* shows far more 
clearly the whole arrangement of a knee-joint of this chai-acter. We owe photo- 
graphs of it in anterior and lateral aspects to Mr S. Steward (see our Plate XXXIV, 
Figs. 89 a and 89 h). They show the sesamoid mounted vertically on the top of the 
fibula and connected proximally by a tendon to the femur above the lateral condyle. 
The sesamoid itself is a true parafibula and does not articulate with the femur at 
all, as is well indicated by the anterior aspect f. In the cases of Bettongia gaimardi, 
Hypsiprymmis murinus, and Myrmecohius fasciatus, we think there is little doubt 
that we are dealing with a parafibular sesamoid and not with a simple lateral fabella. 
Windle and Parsonsj, who have treated at length of the anatomy of Macroj)us 
rufus, state that 
the tendon of the popliteus contains a very strong tibro-uartilaginous fabella, which is placed 
above the head of the fibula to which it is attached, and on which it moves freely. It is with 
this fabella that the large gastrocnemic fabella, to be more fully described in another section, 
articulates. 
And again : 
The outer head of the gastrocnvmius possesses a remarkal)ly \ea-ge fabella already mentioned 
as articulating with that of the popliteus. This "was crescentic in shape [see our Plate XXXV, 
Fig. 90] and in the older sjiecimen measured 2-o cms. from one corner to the other. 
To the muscular attachments as noted by our authoi's we shall return later. 
We are here only concerned with making the point that the cyaniella portion of 
the associated femoro-fibula sesamoidal link of the Marsupials may in certain species 
have degenerated into a cartilaginous§ mass — a hemisesamoid. In cases where this 
hemisesamoidal cyaniella disappears entirely the whole purpose of the fabella- 
cyamella system is lost to sight, and we are provided with a detached sesamoid 
on the lateral condyle associated with a system of muscular attachments which 
formerly were associated with the capituhuii fibulae. 
It seems to us that in the Maisupialia there has been written the complete 
history of the lateral sesamoids of the knee-joint. We have : 
(i) No sesamoids at all but a fibular crest, a continuous part of the fibula 
(some specimens of Wallaby). 
(ii) The parafibula is still fused with the fibula but shows signs of splitting 
into two parts, /a6e//a and cyaniella (certain specimens of Tasinanian Devil). 
(iii) The parafibula separates off as a large lateral sesamoid being an articu- 
lating link between femur and fibula. The two iMirts fabella and cyatuella are still 
united (this is the general rule in the wombat). 
(iv) The large lateral sesamoid breaks up into two components, the fabella and 
the cyamella (this is the case in Didelphys), or : 
(v) The cyaniella becomes a mere hemisesamoid (Macropus i-afus), or : 
* See note t, p. 373. 
t This parafibular sepamoid is not shown in the figured skeleton of the wallaby on p. 130 of Vol. x. 
of the Cambridge Natural History, nor is it referred to in the text; even with Galen of such bones "uon 
est necessarium hoc opere pertractare " ! 
J "On the anatomy of jSlacropus riifus,'" Journal of Anatomy and Physiology, 1897, p. 123 and p. 128. 
§ We much doubt its being " fibro-cartilaginous " as Windle and Parsons state. A section of the 
cyaniella in Macrojjus should be examined as soon as possible microscopically. 
