primrose: the anatomy of the orang outang 
41 
of these marginal structures is increased, because we recognize a large 
number of supernumerary carpals occurring in different parts of the carpus. 
Thus the os centrale is a structure apparently always represented in the 
human embryo, but it soon blends with one of the neighbouring bones 
and loses thus its individuality. We find this bone in the Orang 
remaining separate throughout life. In my specimen it lay between the 
scaphoid, the trapezium and the os magnum. Vrolik^ claims to have 
been the first to describe this bone in the carpus of the Orang. Later 
investigation has proved that in the human embryo a large number of 
carpal elements are often present. Thus Thilenius^ in the human 
carpus in embryos, from the second to the fourth month, found such 
supernumerary bones, all appearing as hyaline cartilage, their structure 
differing in no manner from the normal eight carpals. Thilenius de- 
scribes some thirteen of such. They unite with the neighbouring carpals 
or metacarpals, so that normally in man eight carpals finally result. 
The os centrale may join the scaphoid, the third metacarpal, the trape- 
zoid, or the os magnum. Thilenius found the “ prsetrapezium ” in four 
cases of 113 hands examined, whilst the os centrale was present in all 
cases without exception ; the other supernumerary carpals were present 
only occasionally. Pfitzner,^ in a paper upon the human carpus, 
attempts to group all these supernumerary carpals in the human hand, 
and reconstructs the carpus so as to shew in a diagrammatic fashion the 
position occupied by all these additional carpal bones, and their relation 
to one another. It is in connection with the marginal bones, however, 
that the greatest interest has been aroused, and some anatomists look 
upon the bone described as the prsetrapezium (or the os radiale externum) 
as representing a prsepollex rudiment. Born^ has examined similar 
structures in the tarsus of amphibians. In rana esculenta he figures a 
tarsus in which a supernumerary digit is added on the tibial side of the 
foot. This consisted of three catilaginous elements separated by joints 
and united with a tarsal element which it shared with the first meta- 
tarsal ; a somewhat similar condition was found in Bufo variabilis. 
Emery^ traces various carpal elements in the larvae of amphibia, and 
describes in the anura what he considers to represent the praepollex, 
and the praehallux ; he also demonstrated similar structures in rodents. 
1 Loc. cit., p. 13. 
2 G. Thilenius, “Die ‘ Uberzahlig-en ’ Carpuselemente menschlicher Embryonen.” Anatomischer 
Anzeiger. ix., 1894, p. 663. 
3 Pfitzner, “ Bermerkungen zum Aufbau des menschlichen Carpus.” Verhandlungen der Anatomis- 
chen Gesellschaft. Gottingen, 1893, p. 186. 
4 G. Born, “ Die Sechste Zehe der Anuren.” Morphologisches Jahrbucb, Vol. I, 1876, p. 436. 
5 C. Emery, “ Zur Morphologic des Hand und Fussskeletts.” Anatomischer Anzeiger, 1890, p. 287. 
