178 HISTORY OF THE HUMAN BODY 



carpals [or metatarsals]. These are called radlale and uln 

 \tibiale and fibulare], and the five carpalia [or tarsalia] re- 

 spectively. Of the latter set the individual bones are desig- 

 nated by a number, as tarsale IV , car pale II, car pale V , etc. 

 Aside from these there are two median pieces: the inter- 

 medium, lying between the two proximal elements, and the 

 centrale, distal to it and enclosed by both rows. 



The close similarity that exists between the anterior and 

 posterior limb skeleton, and the frequency with which the two 

 need to be compared, piece by piece, leads one frequently to 

 wish that the nomenclature of the two should be unified 

 throughout, as has already been done in part in the distal por- 

 tion. Probably the chief objection to this lies in the diverse 

 ideas which still exist concerning the serial homology of the 

 parts (treated here in Chapter VI), yet the practical advan- 

 tage that has already resulted from a partial uniform nomen- 

 clature in carpus and tarsus shows the possibility of com- 

 pleting such a scheme as a working hypothesis, without rais- 

 ing the question of serial homology. Such. a scheme is shown 

 in Fig. 47, B, which may be compared with* A of the same 

 figure, that shows the nomenclature now in use. 



In addition to the definite carpal and tarsal bones, which 

 belong to the primary limb skeleton, there are certain other 

 elements of sporadic occurrence, that are situated in or about 

 the tendons of muscles and serve some mechanical purpose in 

 connection with the action of those parts. These are sesamoid 

 bones, and are suggested in the diagram by dotted lines. Of 

 these the most usual are a radial and an ulnar one [tibial and 

 fibular] placed upon the free edges of the carpus [or tarsus]. 

 Sesamoids also occur in other portions of the limb skeleton; 

 thus the patella, constantly found in birds and mammals, oc- 

 curs in the posterior limb between the first and second long 

 joints, and forms the protuberance at the knee. Small sesa- 

 moids, often associated in pairs, are found on the flexor side 

 of the digits between the phalanges. 



Although the above scheme for a typical carpus or 

 tarsus and its nomenclature seems to serve the purpose 

 of naming the parts in all cases (Fig. 48), there are man 





