OF GALLINACEOUS BIRDS AND TINAMOUS. 217 



of the Tinamou. This bone, the prevomer, is not a rhinal element — a true turbinal, 

 nor the homologue of the prefrontal of the fish (see Owen, Report on Archetype, p. 220), 

 but a splint applied to the cartilaginous floor of the anterior nostril, and only existing in 

 birds and certain groups of Reptiles, and in the Amphibia. In the Tinamou the pre- 

 vomer runs forwards as a sharp wedge between the palatine process and the dentary 

 margin of the premaxilla, to within 7 lines of the end of the beak : it is made of just the 

 same delicate fibrous bone (PI. XL. fig. 1). It gradually becomes 2 lines in width, and 

 then divides into a long zygomatic and a short palatine process : close behind this 

 bifurcation the zygomatic process thickens and gives oflF two secondary processes, one 

 upwards, which articulates, as we have seen, with the descending crus of the nasal, 

 and one inwards, a flat zigzag band of bone (PI. XL. figs. 1 &2), which becomes pedate 

 and then articulates with the anterior part of the palatine, by curving downwards and 

 applying itself to the inner edge of that bone. On the whole, the bone of the Tinamou 

 agrees closely with its counterpart in the Ostriches ; yet the inner process is some 

 approach to the same part in the Grouse and the Sandgrouse ; but in them the body of 

 the bone is reduced to the smallest dimensions, and the inner process passes far more 

 mesiad of the palatine bar, and is free and straight, although pedate. In the Ostriches 

 the inner process is scarcely differentiated from the rest, and the body of the bone in 

 them is of most unusual size. The ascending process of the prevomer is the homo- 

 logue of that curling outward part of the bone in the Python which seemed to Professor 

 Owen to have " a neurapophysial relation with the olfactory nerves " (ibid.). 



Our author atones for this mistake, at the top of the next page, by satisfactorily deter- 

 mining the great preorbital bones of the Python to be merely the lachrymals, and not 

 the " anterior frontals " as Cuvier supposed. 



Across the mid region of the palate of the Tinamou there has been an unusual 

 amount of anchylosis even for a bird (fig. 2) ; and here we impinge upon the Apteryx 

 in a manner not to be misunderstood. This is the more interesting, as this bird is four- 

 toed ; and if any one will also compare the leg and foot of the two birds, they will see 

 how very gentle a change is required to convert either the leg or the beak of an Apteryx 

 into that of a Tinamou. 



The zygomatic process of the prevomer has coalesced with the slender jugal (PI. XL. 

 figs. 1,2, 3), and this latter hone reaches, as in other " Struthionidse," nearly to the os 

 quadratum, the quadrato-jugal being a small piece of bone passing somewhat within the 

 jugal ; it is, however, separate in the adult. These bones vary greatly in different birds, 

 and in the Fowl-tribe the quadrato-jugal reaches nearly to the angle of the premaxilla. 

 Where the maxillary exists at all, it is quite external to the prevomer, which is always 

 placed mesiad of the dentary part of the premaxilla, of the maxilla itself, and of the 

 quadrato-jugal. The absence, for the most part, of the maxillary gives rise to an 

 extraordinary and somewhat vicarious development of the prevomer in birds. In the 



2 f2 



