218 MR. W. K. PARKER ON THE OSTEOLOGY 



fledgeling Heron {Ardea cinerea) , the palatine part of the prevoraer reaches to within an 

 inch of the end of the beak, and the zygomatic part to within a quarter of an inch of the 



05 quadratum, — its whole length being nearly 4 inches, the entire head at that time not 

 being more than 5 inches 8 lines : compare this with the prevomer of the Amphibians ! 

 The " vomer " of the Tinamou (PI. XL. fig. 1) is full an inch long, and a line wide at 

 the narrowest part ; in the Rhea (PI. XL. fig. 1 , v.) it is more than 2J inches long and 

 3 lines broad at the middle ; the form is the same in both, and the relative size the same, 

 but it is slenderest in the Tinamou. It forks in front in both, and these forks are 

 underlain on each side by the palatine processes of the premaxillaries (PI. XL. fig. 1, 



6 PI. XLIL fig. 1, v.px.): in both cases it forms a splint-like sheath to the great 

 basisphenoidal rostrum, which appears in front between and above the forks (PI. XL. 

 fig. 1, & PI. XLIL fig. 1, r.hs.). How far this is from the structure of any gallina- 

 ceous bird I need not say, where the vomer is extremely delicate and small, and the 

 " rostrum " short (PI. XXXVI. fig. 6.). 



In the Weka-Rail (Ocydromus) and in the Lapwing {Vanellus), the shorter " rostrum " 

 lies in the vomerine groove (PI. XXXVII. fig. 1, v.bs.) ; but it does not in either case 

 reach the middle : still these birds have vomers and " rostra" more in harmony with 

 those of the struthious birds than the Fowls have. On one hand, the large, single, 

 semicylindrical vomer of struthious birds comes near that of the mammals ; on the 

 other hand, it is unmistakeably like the single vomer of the Chelonians — having, like 

 them, a broad anterior part on a lower plane than the rest and articulating with the 

 premaxillae, a middle constricted part separating the middle nares from each other, and 

 a posterior expanded part sheathing the cranio-facial axis, and articulating with the 

 posterior end of the palatines and the anterior end of the pterygoids' (PI. XLII. 

 fig. \,v.). The posterior broad end of the Tinamou's vomer does not keep free as in 

 the Great Ostriches, but agrees with that of the Apteryx in coalescing with the ptery- 

 goids and palatines. It is very common for the vomer to keep distinct from the pala- 

 tines in the Rails, Plovers, and in many both wading, swimming, and diving birds ; but 

 in a large number of the other great groups the posterior forks of the bone rapidly 

 coalesce with the interior edge of each palatine, where they are sheathing the " ros- 

 trum." But it is only, as a rule, in certain birds of a high and noble kind that we 

 meet with a coalescence of the palatine elements to such a degree as to involve the 

 pterygoids also. The Tinamou has this character ; the Apteryx has it ; and then we 

 must pass to the three main divisions of the great typical group to find this state ot 

 things again. I have found this coalescence in the following birds : — 



' Amongst the typical birds, the Falcons {Falco), the Dicholophus, the Sacred Ibis {Threskiornis ceihiopicus), 

 some of the " Meropidse," the Wild Duck {Anas boschas), and especially the Albatros (Diomedea exulans) 

 come near the Chelonians in the condition of the vomer ; in all these, however, the vomer is separated more or 

 less from the palatines by the intervention of an additional segment on each side, viz. the " mesopterygoids." 



