3._0N THE NOMENCLATURE OF THE ELEMENTS OF THE 

 AMPHIBIAN SHOULDER-GIRDLE. 



By R. Broom, M.D., D.Se. 



It is rather surprising tli;it at this late period there should be so 

 much confusion in the names of the elements of the frog's shoulder- 

 girdle, moie especially as the frog is tlie type of vertebrate more 

 studied by students than any other. There is at present not a single 

 element in the frog's girdle or sternal appai-atus concerning which thei'e 

 is not some difference of opinion. 



In the frog there lies in front in the middle line a structuie for 

 the most part ossified behind and anteriorly expanding into a little 

 cartilaginous disc. If the student turns to his ordinary te.xt-books 

 he finds the following confusion. Thomson, Reynolds and others call 

 the bony portion onwfitfirniini and the cartilaginous part epi'<terHum : 

 Wiedersheim calls the whole structure omosteruuni : while Parker and 

 Haswell call the bony part epl^ternum and the front part oinosteruum. 

 .Sedgwick calls the whole omo.sternum, but in brackets gives as synonyms 

 episternuni and presternttni. What the homologies of the structui-e are 

 no one knows for certain, and whether it may be homologous with the 

 little cartilages in front of the mammalian sternum or not need not at 

 present conceiii us, as the name oDiosternum was originally apj)lied to 

 the whole structure by Kitchen Parker over forty years ago, and what- 

 ever structures may afterwards prove to be homologous \\ill have to 

 take this name. All the confusion has arisen through the most un- 

 fortunate introducti(m into zoological literature, I believe by Gegenbaur, 

 of the term episternnni. This term he gave to the median bony element 

 of the shoulder-girdle of the lizard and to any other element that seemed 

 to be in a similar position. Though Paiker in 1S68 had clearly eluci- 

 dated almost every d(!tail of the structure, the infivience of Gegenbaur 

 gave rise to a confusion from which only a very few writers of text- 

 books in even recent years have been able to free themselves. There 

 can now be not a shadow of a doubt that Parker was right in regarding 

 the median nienibrane l)one of the lizard, which h(> (-ailed the iii/er- 

 dmiicle, as in no way ho)nologous witli the cartilage element found in 

 the fi'Og, and to call the two elements by the same name, >'j>ist''i'anin, 

 can lead to nothing but confusion. The latest text-book which J ha\c 

 at hand is Sedgwick's Student's Text-book, Vol. II, published in 1905. 

 Here on p. 270 omosteriium (epistenmm, pye-sfenutm) is the name given 

 to the median elenient of the frog, but on the following page pp'n<tfrni'm 

 (omos/eniiDu) is used. On p. '.)] t the Stegocephali are stated to have 

 i/iitp.rrl(inidf,>i. On p. 320 the term htteylavicl'' is again used in de- 

 scribing the structures in the l^eptilia, and this term is retained 

 throughout the work, except oji p. 339, where bitei-rJavicle {episternam) 

 is used. Naturally a stu<lent would be led to believe that the 



