358 
On the Sesamoids of the Knee- Joint 
amphibius, the water vole); Leinmus obensis (Siberian, ? Norwegian, lemming), 
internal somewhat larger ! Fiber zibethicus (musquash), external large and internal 
small; Dipus jaculus Alactaga jaculus); Spalax typhliis (mole rat); Lepus 
timidus* (hare), external in facet on external condyle, internal in groove, but this 
may happen with external ; Lepus ciunculus (rabbit), internal small as compared 
with external ; Cavia (guinea-pig), external larger ; Dasyprocta aguti, both as hemi- 
sesamoidsf (hyaline cartilages). On the other hand in a young specimen' of Castor 
fiber, he found neither and this was also the case in Cercolabes prehensilis (tree 
porcupine), although gastrocnemius was very fully developed. In M. glis Gruber 
found the external fabella only, articulating on condyle. He examined three kinds 
of Gricetus (hamster) and found in one both fabellae, in a second the external only, 
and in a third neither. 
We now come to our own investigations. In the authorities cited above we have 
no records of the presence -of the cyamella and only the single reference of Owen to 
the presence of a lunula in the squirrel. 
A dissection of the common rabbit showed both fabellae and the cyamella but 
no lunula (see Plate XXIV, Fig. 58). In a mounted skeleton, however, we found 
both fabellae, the cyamella and both anterior lunulae. A dissection of the common 
squirrel (two specimens) showed both fabellae, the cyamella and an anterior mesial 
lunula (see Plate XXIII, Fig. 55 b). In a third very young squirrel the lateral fabella 
was found, but no mesial had yet developed (no microscopic examination made) ; 
the lumda y^as well developed |. In the African squirrel {Paraxerus jacksoni) we 
found both fabellae, the cyamella and the anterior mesial lunula (see Plate XXIV, 
Figs. 60 a and 60 6). 
In the domestic mouse both fabellae and both anterior lun ulae but no cyamella 
were found ; the smallness, however, of the knee-joint renders (without microscopic 
examination of sections) the discovery of the sesamoids rather precarious. 
In the musk rat {Fiber zibethicus) we found hoVci fabella,e, two anterior lumdae, 
of which the mesial is under the ridge of the patellar depression, and one posterior 
lateral lunida. There was no trace of a cyamella, and it is possible that it does not 
exist in the musk rat or is replaced by this posterior lunula (see Plate XXIV, Figs. 
61a and 61 b). 
Turning to mounted specimens we found both fabellae in the following : Trichys 
guentherai (Gunther's porcupine), Lagostomus trichodactylus (Viscacha§) in two 
specimens, Thrynomys sivinder-nian us (cave rat), Mus fuscipes (brown-footed rat), 
Mesembriomys hirsutus (Gould's jerboa rat), Microtus amphibius (water vole), 
Alactaga decumana, (Kirchig jerboa), Alactaga acontium (Siberian jerboa), 
Spermophilus guttatus (a souslik), Sciuropterus volucella (North American flying 
* Mivart and Murie, Vroc. Zool. Society, 1866, p. 413, state that the hare differs from the guinea-pig 
by having neither fabella {\). 
t We have found orthosesamoids in our specimen. 
J We also found only the lateral fabella in a mounted specimen of the common squirrel, but this is 
hardly evidence even of the occasional absence of the mesial. Cf. Meckel's statement p. 357. 
§ There is a double-sized lateral and a smaller mesial fabella. 
