28 Mr. W. A. Forbes on the late Professor Garrod's 



there adopted. Nevertheless I think I may say he was 

 satisfied to the last as to the naturalness of the two main 

 groups into which he there divided birds^ the " Homalo- 

 gonatse^^ and the ^^ Anomalogonatse.^^ It is often assumed 

 that this division rests only upon a single character^ namely 

 the presence or absence of the ambiens muscle. As a matter 

 of fact this is ?iot the case ; for the ambiens muscle is absent 

 in many birds that are ranked amongst the Horaalogonatse. 

 What Prof. Garrod says is this : — '' The oft-named ambiens 

 muscle isj in my mind^ the key to the whole/^ and that; not 

 because of its own intrinsic importance^ but because its pre- 

 sence is always associated with peculiarities in other parts 

 never found in any Anomalogonatous bird. That the same 

 combinations of three or four different characters should have 

 arisen independently in different birds is so extremely impro- 

 bable^ that we can hardly ascribe these similarities in com- 

 binations of characters to any other cause than to blood- 

 relationship; the expression of which is now unanimously 

 accepted as the true end of all biological classifications. 



" The facts disclosed by a study of the myology of birds 

 do not, without extraneous assistance, place the families in 

 their true relationship to one another. Because the same 

 muscles are present in two families of birds, it cannot there- 

 fore be said that their kinship is extremely close, or the re- 

 verse .... It is therefore necessary to look around to find, 

 if possible, myological characters which have some definite 

 relations to equally Avell-marked pterylographic, visceral, or 

 osteological peculiarities^' (P. Z. S. 1874, p. 114). As 

 already insisted on, it was in this combination of charac- 

 ters that Prof Garrod trusted to find the true " key " to the 

 question. 



To return to facts, — no bird which is ^^Anomalogonatous " 

 has ever an accessory femoro-caudal muscle; that is, the 

 letter B never enters its formula. Again, no bird that is 

 Anomalogonatous has ever a tufted oil-gland and cseca, 

 though this combination is nearly always found in the Homa- 

 logonatous birds. So much so is this the case, that there 

 are only nine groups of Homalogonatous birds that have not 



