Karl Pearson and Adelaide G. Davin 
898 
without ossified patellae. If it be argued that this depends on a difference of mode 
of progression, a similar counter can hardly be made to the arguments adopted in 
favour of a use value for the fabella ; these arguments are too strong, the Anthro- 
poidea ought never to have lost their fabellae ! If we take what appears to us the 
more rational view that all the sesamoids of the knee-joint are vestigial, and are 
debris of one or more structures originally of use value, we are bound to consider 
some such scheme as that of the accompanying diagram, and then the chief difficulty 
of linkage is seen to be at once apparent in the question as to how far the sesamoids 
in the knee-joint of any existing species are to be accounted for by accpusition or 
lapse. For example, the bear and the sheep possess the patella alone : are we to 
assume their ancestors have never possessed or have lost a complete system ot 
knee-joint sesamoids ? The frog and some species of bat possess no sesamoids at all 
of the knee-joint, but the former has never acquired them, and in the latter they 
have been suppressed in a long course of evolution. So it is with sheep and bear ; 
the former belongs to the Ungulates who give no evidence of ever having developed 
a knee-joint sesamoid* beyond the patella, and the latter to the Carnivores with an 
elaborate evolutionary history of knee-joint sesamoids as complex as that of the 
Rodents or Insectivores. Again those who like Abel assume the Pinnipedia to 
have sprung from the Ursidae-f- seem to overlook the relationship of the latter to 
the full knee-joint sesamoid system of the Carnivores — especially to the Canidae. 
Or, to go a stage further, we have so far not come across any Insectivores with 
patella only. Edentates of this character exist, but the Insectivore with only a 
patella has yet to be found. It may have existed, but the Insectivores seem to 
have sprung from a multi-sesamoidal form. Chiroptera and Rodentia can well 
have sprung from the Insectivores. To suggest as Kukenthalj that the Ungulates 
sprung fi'om the Insectivores and the latter from Marsupials, is to neglect the 
fundamental contribution of the Marsupials to the knee-joint sesamoid system, 
namely, the cyamella and the lateral fabella. The parafibula is known in reptilian 
forms and the Edentates may have got their parafibula from these. But if the 
Ungulates sprung from the Marsupials it is astonishing that no cases even as 
anomalies of the cyamella in the Ungulates have been recorded. 
We may note also a very special point of difficulty about the Marsupials them- 
selves. An ossified patella is an extreme rarity. Are we to assume that the patella 
was lost in the Marsupials while cyamella and fabellae were developing ? The 
ossified patella exists in the Monotremes, and this alone would differentiate them 
largely from the Marsupials. But if the patella was obtained in the reptilian stage 
and handed on to the Monotremes and certain birds, while it was lost in the Marsu- 
pials, it is hard to believe in a direct descent of Insectivores from Marsupials, at 
any rate it would point either to the Peramelidae or to some other Marsupial differ- 
ing widely — as far as the knee-joint is concerned — from those hitherto known. 
* The lateral /afeeiZa of Hyra.x we take to be evidence, not of a lost sesamoidal system in the Ungu- 
lates, but of a differentiated origin of Hyra.r. We liave not been able to confirm Meckel's and Gruber's 
statements as to the Cervidae. 
t Handworterbitch der Naturwissennchaften, Bd. viii. S. 718, 1913. + Ibid. Bd. viii. 
25—3 
