220 MR. W. K. PARKER ON THE OSTEOLOGY 



palatines and the pterygoids could scarcely have been simpler ; they bound the large 

 middle nares behind, and laterally for some distance, and through the intervention of 

 the overgrown prevomers they connect the palate with the zygoma. 



We must look to another group to yield us anything like that curious prolepsis of 

 the mammalian posterior nares which is seen in the Crocodiles. The Finches just men- 

 tioned, especially Estrelda, have a condition of the palatines and pterygoids not far 

 from those of the great reptiles, as it respects the posterior nasal canal ; the tube is, 

 however, imperfect for its lower third. The sphenoidal facet on the Tinamou's ptery- 

 goid has been mentioned already ; that which hinges on to the os quadratum is a 

 miniature of the concavity on the ulna of the mammal for the reception of the con- 

 dyles of the humerus. As in the other " Struthionidse," the lower edge of the Tinamou's 

 pterygoid is thick, the upper thin and sharp. The only real difference between the 

 bones of the subtype and the type is the slenderness of those of the former, combined 

 with a somewhat more elegantly ornithic form — a more delicately moulded condition 

 (Pis. XL. & XLII. fig. 1). 



If we look to escape from the struthious type in the " os quadratum" of theTinamou, 

 we shall be mistaken ; and not only is it struthious in character, but, like its counter- 

 part in the great Ostriches, it is only barely ornithic (figs. 1 & 3) ; the superadded 

 orbital process (which is lost again in the " incus" of the mammal) and the characters 

 of the hinge for the mandible are its saving qualities, and connect it with its typical 

 condition in the higher classes of birds. The facets on the base of the os quadratum 

 are like those of the larger " Struthionidae," the outer having somewhat the shape of a 

 kidney, with the hilum looking inwards and forwards ; the inner convexity is irregu- 

 larly ovoidal, the broad end being outwards, and the narrow end passing inwards and a 

 little forwards. Above the inner end of this facet is a trochlea, on which the concave 

 end of the pterygoid is hinged. These condyles are very unlike those of the " Gallinse" 

 (PI. XXXVI. fig. 6). but they are nearer those of the Rail and Plover (PI. XXXVII. 

 fig. 1,5.): in them the inner facet somewhat resembles the condyle on the anterior 

 end of the cervical vertebrae of birds, being convex across and concave from side to 

 side ; they are still more like the upper articular face of the astragalus of the Sheep 

 and Ox, as the scooping is oblique, and not square with the ends of the trochlea as 

 in the bird's vertebra. The orbital process is almost as elegantly formed as in the 

 Plover ; it is, however, narrower than in that bird, or the great Rails, or its own con- 

 geners. That narrowing is important, as it is one more very faint gallinaceous character 

 in the head of the Tinamou. But the head of the bone is the most important cha- 

 racter, and from it alone the anatomical expert might have determined the struthious 

 nature of the bird owning it. There is but one facet, a very long oval in shape 

 (PI. XL. fig. 3), with the outer side scooped' somewhat, as in the Rhea ; this convex 

 facet is a better oval in the Emu. Its long axis is not parallel with the axis of the 



' Precisely as in the LacertiUa. 



