392 
On the Sesamoids of the Knee- Joint 
recorded in reptilian forms*, and we do not know to what extent the inner head of 
gastrocnemius is associated with this crestf. The possibility of the cnemial crest 
having given rise to either or both patella and mesial fahella may indeed be borne 
in mind, but it is not of a high order of probability. One feels inclined to propound 
some general ontogenetic principle by which what occurs by evolutionary origin on 
one side of a member will be " sympathetically " (or cytologically ?) shadowed on 
the other. Thus lunidae, fabellae or even condyles occur in pairs, and this is true 
also of nauscular attachments and tuberosities. To propound such a principle would, 
however, be too venturesomej, and all we can assert is that the mesial fahella has 
certainly a different origin to the latei'al. It is later in arriving and earlier in 
degenerating and never has the anatomical importance of its lateral colleague. 
(24) Conclusions. 
The main point that seems to us to arise from this study of the sesamoids of 
the knee-joint is that no parts of the mammalian skeletal form, however apparently 
insignificant, are without exceeding interest if time can be devoted to their study. 
If we take the whole evolution of the sesamoids of the knee-joint from their entire 
absence in the Amphibia to their culminating point in the Tupaiidae and Sciuridae 
and to their entire disappearance in certain Pteropodidae, we are compelled to 
admit the feebleness of the argument for use value in any case but that of the 
patella. Even in the case of the patella we have to admit that the Amphibia, many 
reptiles, the Marsupials, and some birds seem to have got on remarkably well 
* The occurrence of reptilian forms with even moderate tibial crests should be of a very exciting 
character. The only case we have so far been able to discover is that of Ceratosaurus nasicornis Marsh, 
a carnivorous Dinosaur of the American Jurassic. It is figured by Marsh and the tibia has a large 
cnemial crest. It shows in certain respects other avian resemblances as in the form of the pubis and in 
the co-ossifications of all the pelvic and of the metatarsal bones : see " The Dinosaurs of North 
America," by 0. C. Marsh, Sixteeiitli Annual Report of the U.S. Geological Survey, Part i. pp. 156 
—162, and Plate XIV, 1896. 
t E. Coues in his paper on "The Osteology of Cohjmhus torquatus, with notes on its Myology" 
{Memoirs of the Boston Society of Natural History, Vol. i. 1863, pp. 131 — 172) deals with muscles of the 
knee-joint. In this case the tibial crest is as long as the femur itself (2") : see our Plate XXXVI, Fig. 94, 
and the author makes no mention of an independent patella. Indeed he writes (p. 159) : " Just at the 
border of the joint there is a very small projecting process of bone, which is generally regarded as the true 
analogue of the patella." Of the muscles he states that Cruracus has a very extensive muscular attach- 
ment to the posterior face uf the whole length of the tibial spine which projects above the knee-joint 
(p. 168). Semimembranosus is inserted by a broad membranous tendon into the crest of the tibia (p. 170). 
Gastrocnemius might, it seems, almost be described as having four heads. Part of the inner arises 
fleshy from the apex of the tibial spine and from the anterior face of the upper two-thirds of the bone, 
the other portion of tlie inner arises from the inner condyle. The outer head arises from the linea aspera 
for nearly two-thirds of its length and from the outer condyle ; it also receives attachments from the 
rectus femoris (p. 171). But the rectus femoris instead of going to the patella as in man is inserted in 
the head of the fibula (p. 167). It would thus appear that the inner head arises from inner condyle and 
tibial crest, the outer head from outer condyle but is linked also to head of the fibula. The femur 
articulates with tibia and fibula; the articulation of inner condyle is tibial; that of outer condyle partly 
tibial, but most extensively fibular (p. 159). Without being conclusive this description is most suggestive 
for the possibility of the origin of the patella from the tibial crest and to a lesser extent of the origin 
of a mesial fahella from the same source. 
} The tendency, however, to reach greater complexity by doubling may, perhaps, be traced in various 
organs, e.g. in the olfactory organ, or the evolutionary history of the ventricle of the heart. 
