14 NATURAL HISTORY OF BIRDS. 



ratio of the fillicrs iliTvonsiiig gradually toward the ends. I5y progressive specializa- 

 tion the niiinliir of ])halangcs is often reduced, e.jr., in some swifts which have oidy 

 two, three, tliree, an<l three phalanges respectively, and the proj)ortion of their lenr;th 

 modified. 



Concerning the nuisdes of birds, we should like to enlarge upon the mechanism 

 moving the wings, ;ind that wonderful arrangement hy which the toes of the perching 

 liird are automatically kept in a grasping p(jsition Ity means of the bird's own weight 

 alone ; but want of space i)ermits us only to mention and e.\idain a. few teclinical terms 

 and signs which will be found useful further on. The late Professor Garrod used tlie 

 letters A, B, X, and Y to represent certain muscles of tlie thighs which he consiilered 

 to be of particular taxonomic value, viz., respectively, the femoro-<-:milal, the accessory 

 femoro-caudal, the semi-temlinosus, and the accessory semi-tendinosus; thus, saying 

 tliat the muscular formula of the secretary bird is BXY means that the three latter 

 are]iresent. The formula A in the falcon nutans that none but tlie first-mentioned is 

 to l»e foun<l. 



Besides the above, two <ither muscles belong to the femoral region of ))irds, the 

 account of which we sliall give as nearly as jiossible in the late Professor Forbes's words, 

 viz., the f/fiitciis primus ancl the (Oii/n'i us. The former is, as a rule, not small, and is only 

 seldom .'iliseiit, c.;/., in (he Bucenitiche and Palanudciihe : the latter, the iniibiois, lies 

 on the lower or inner sin-face of the thigh. As generally (levelo]ied, it is :i more or 

 less sleniler fusiform nmsde, which, arising from the pra'pubic j)rocess of the ]ielvis, 

 close in ficiiil I if till' acitabiiliini, runs along the inner side of the tliigh sujierficially, and 

 then, as a thin tendon, over the benil of the knee — in some cases jierforating the 

 patella — to the outer side of the leg, terminating thereby joining one of the tendons 

 of tlie suj)erticial flexor of the toes. In all ])asserine liirds, and some others, it is 

 always absent ; these are termed anonialogonatous birds, in contradistinction to the 

 more generalized types which are liomologonatous, and wc denote the presence or 

 absence of the aiuhkiis muscle by the signs -|- or • — . 



In all birds there are two deep fle.vor muscles of the toes, the tendons of which 

 run along the posterior (plantar) aspect of the metatarsus, one the deep flexor of the 

 iiist toe {/. loiif/iis /la/h/ri.i), the other closing the remainder of the toes, fh.ror per- 

 fiirans dir/ilonim, the former being always external to, or sujicrficial of, the latter 

 when ]iassing the metatarse. In all Passeres and a few other birds, e.r/. I'juijMr, these 

 tciulons are (luite inde])endent of each other, so that if tlie flexor of the iirst toe be 

 artiticiallv ]iiilled, no closing (flexion) of the other ones takes jilace. In all other birds, 

 however, till' two tendons are more or less intimately connected by a lilirous Iianil 

 {viiiculioii), or maj' even completely lilend. 



]$y far the most interesting feature, liowever, brought out by I'rof. (iarrod's inves- 

 tigations into this subject is the discovery of the existence of the entirely different 

 types of jilantar arrangement in the so-called zygodactyle birds (witli usually two toes 

 in front and two turned backward), as well as the fact that the diversity of typo 

 exactly coinciilcs with the two grou])s of birds so marked out, beiiif; res]iectively homolo- 

 and anomalo-gonatous. Thus in the jiarrots, cuckoos, and ]\Iuso]iIiagida', which all 

 belong to the former group, the jdantar tendons are distributed in exactly the same 

 way as in the common fowl, the JJcrar pcrforans sup])lying second, third, and fourth 

 digits, and the./! IkiIIucIs the first digit alone. In all the anonialogonatous zygodac- 

 tyle birds (all of which lack the ninbiens and accessory femoro-caudal muscles) namely 

 the Pieida?, Capitonida', ami their allies, Biiccdniihe and Oalbiilida', an intirely uni(]ue 



