450 MR. A. H. GARROD ON THE [May J 5, 



colaptes albic.ollis, Picolaptes affinis, Thamnophilus murinus, Tham- 

 nophilus doUatus, Thamnomanes glaucus, Grallaria guatemalensis, 

 Hylactes megapodius, Pteroptochus albicollis, or any other Passerine 

 bird with which I am acquainted. They are, in fact, schizorhinal, 

 like the Charadriiformes ; in other words, the osseous external nares 

 are in the form of triangular openings, the apical angle of each of 

 the triangles being situated between the inner and outer process of the 

 nasal bone of the corresponding side'. Figure 3 gives a view of the 



Fig. 3. 



Superior surface of skull of Fimiariiis nftcs, to show the schizorhinal form. 



upper surface of the skull of Furnarius rufus. It has been my habit 

 to group all the birds possessing the schizorhinal skull in a single 

 major division, including the restricted Limicolse, the Gruidse, Laridse, 

 Alcidse, and the Columbidse ; but the independent development of 

 an identical disposition in the small division of the Passerine birds 

 above mentioned weakens the importance of the character to a 

 certain extent, although it is not at all necessary to assume that it 

 overthrows its significance. Collateral evidence, from visceral and 

 other details, compels me still to think that those schizorhinal birds 

 which possess the ambiens muscle — or are, in other words, homalo- 

 gonatous^ — must be retained in one great order, the Charadrii- 

 formes, until some important structural differences are discovered 

 which necessitate their being otherwise arranged. The schizorhinal 

 disposition is most certainly one which is a secondary development 

 upon the normal holorhinal nares ; and that it has been independently 

 arrived at in two non-related orders of the class is proof that it re- 

 sults from most simple causes, because the probability that the same 

 complex conformation should appear de novo varies inversely as the 

 complexity : the greater the elaborateness the less the chance that it, 

 in all its detail, comes into existence more than once. A still more 

 simple variation is found in the number of the carotid arteries, the 

 normal two being reduced to the left only in certain members of 

 ' Vide P. Z. S. 1873, p. 33. ' Vide P. Z. S. 1874, p. llfi. 



