350 PROFESSOR OWEN ON THE GENUS DINORNIS. 



compressed angular plates, with the angle rounded off ; the lower portions (fig. 3, s') 

 expand into thick rough surfaces which appear to have been capped by cartilage. 

 At the anterior end of these surfaces, which are but two lines apart at the middle 

 of the basisphenoid, that bone rises abruptly at an acute angle for the extent of 

 half an inch before it reaches the base of the presphenoid, from which it is detined 

 by a transverse groove (fig. 3, e) passing between the two outlets of the osseous parts of 

 the eustachian tubes. The fore-part of the basisphenoid is similarly defined in Otis 

 (fig. 8) ; but its under surface is flat, with two tuberosities posteriorly. It ofiers, however, 

 a certain resemblance to the basisphenoid of Dinornis, in the presence of a broad ridge 

 on each side (s") connecting the basisphenoid with the paroccipital processes. The basi- 

 sphenoid in Didiis presents a longitudinal channel bounded by parallel lateral ridges ; 

 the sides of the basisphenoid which incline to these ridges are slightly concave, have 

 two perforations posteriorly, one above and a little in advance of the other, and form 

 the anterior and inner boundary of the tympanic cavity. 



The fore-part of the wedge-shaped basisphenoid in Dinornis presents a smooth sub- 

 quadrate surface convex forwards from side to side, hke a half-cylinder. There is a 

 median vertical depression on the basioccipital, a little below the condyloid peduncle; 

 and three minute foramina (fig. 4,v) on each side the base of that peduncle. 



The precondyloid {p) and carotid (c) foramina open externally into a large fossa 

 common to them and some pneumatic holes communicating with the diploeof the exoc- 

 cipitals immediately external to the back part of the lateral basioccipital ridges : there 

 is a similar depression for the two foramina on each side in the Dodo and the Bustard. 

 The exoccipitals send each a small tuberosity inwards where they form the sides of the 

 foramen magnum (fig. 4, o), which sides expand and are impressed by a well-marked 

 vertical groove for the ' sinus occipitalis ' behind those tubercles, which have a narrower 

 groove in front of them. The form of the foramen is that of a vertical ellipse with 

 straight sides : its upper border is continued on each side downwards and outwards upon 

 the obtuse angle dividing the exoccipital (2) from the paroccipital (4) surfaces ; the angle 

 terminating below in a short process or ridge bounding a muscular impression. This 

 impression is continuous with other roughnesses for muscular attachment extending 

 over the whole inferior irregular surface of the paroccipital. This surface (figs. 3, 6, 4') 

 abuts upon the outside of the basioccipito-sphenoidal plate (5'), and widens as it extends 

 outwards to terminate in a concavity on the under part of the paroccipital angle (4, fig. 3): 

 its smaller mesial or inner end offers a rough articular surface for the stylohyal (as), which 

 was anchylosed to this surface on one side (as shown in figs. 3 & 6) : there is a tuberosity 

 (4', fig. 3) midway between the outer and inner ends. The extent of the paroccipital, to 

 which the great breadth of the occipital region is due, is a striking characteristic of the 

 Dinornis. The foramen magnum is longest vertically in Didus with lateral processes 

 encroaching upon it, but the upper half so defined is narrower than in Dinornis and almost 

 pointed above; the margin of the foramen is broad and excavated; it is perforated above 



