TO BIRD-ANATOMY AND CLASSIFICATION. 209 



The other group, the Mesomyodi, have the intrinsic muscles (which Ibis, 1881, 

 are usually reduced to a single pair, one on each side) inserted into the 

 middle of the rings. In them, too, the tenth (" first ") primary is always 

 more or less long, and the tarsus, with trifling exceptions, not " bila- 

 minate." They nearly correspond to the " Formicarioid " Passeres of 

 Wallace, except that Wallace included in that group the Acromyodian, 

 though in some respects aberrant, Menura. The Mesomyodi include all 

 the Tracheophone Passeres, together with the Pipridse, CotingidaB, Tyran- 

 nidaD, Pittidae, and a few smaller groups. A further division of these 

 two main groups is given by Prof. G-arrod in the first paper quoted (t. c. 

 p. 518), the smaller divisions being based on one or other of the other 

 characters already noticed. A considerable number of the previously 

 unknown syringes of Passerine birds were described by him for the first 

 time in one or other of the above communications, amongst which those 

 of Pitta and Atrichia are particularly noticeable. The peculiar form of 

 the nasal bones in certain of the Tracheophonae, so that these birds are 

 to this extent " schizorhinal," has already been mentioned when speaking 

 of that character, as has also the paper on Heteralocha. 



It is much to be regretted that Prof. G-arrod did not live to make 

 public his maturer v r iews on the difficult subject of the general classi- 

 fication of birds. The only published scheme of any such classification 

 is to be found in part ii. of his paper on the Thigh-Muscles (supra, p. 194) ; 

 and it is within my knowledge that he had already seen reason to deviate 

 in some respects from the arrangement there adopted. Nevertheless I Ibis, 1881, 

 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 " Homalogonatao " 

 and the " Anomalogonatae." It is often assumed thab this division rests 

 only upon a single character, namely the presence or absence of the 

 ambiens muscle. As a matter of fact this is not the case ; for the 

 ambiens muscle is absent in many birds that are ranked amongst the 

 Homalogonatae. What Prof. Garrod says is this : " The oft T named 



of an " Acromyodian " syrinx, these birds depart essentially from the typical avian 

 " Mesomyodian " structure, the one which there cannot be the slightest doubt is the 

 more primitive form. "The much more important osteological characters" in which 

 these two forms are said to diverge from the other Passeres are, as far as I am aware, 

 two only ; and these, moreover, are individual peculiarities of each genus, and by no 

 means common to the two forms in Menura the curved posterior margin of the 

 sternum, in Atrichia the absence of clavicles (Garrod, P. Z. S. 1876, p. 516). As is now 

 well known, Prof. Huxley's original description of the skull in Menura (P. Z. S. 1867, 

 p. 472) was founded on a misconception of its structure, apparently owing to the im- 

 perfection of his specimen (cf. Parker, Trans. Z. S. ix. pp. 307, 308). Moreover the 

 "most anomalous forms of Passerine birds yet known," or at all events the most 

 generalized, are, according to the views of Garrod and myself, certainly the Eurylamidfe, 

 which last therefore, and not the " Pseudoscines," should be placed at the end, in a 

 descending scale, of the Passerine series. 



