PEOPESSOE OWEN ON THE GENUS DINOENIS. 179 



In Apteryx australis there are nine caudal vertebrae, the anterior ones of greater 

 relative vertical extent than in St rut hi oni dee ; but as they recede they gain in transverse 

 and lose in vertical diameter. The last two coalesce to form the ' ploughshare ' bone. 



FORTY-FIRST, or SECOND CAUDAL VERTEBRA (J nat. size). 

 Fig. 36. Fig. 37. 



Aspects. 

 Fig. 36, preaxial ; 37, lateral. 



I am not certain that I possess the fortieth vertebra or ' first free caudal' va. Dinornis. 

 The second, if it be not the first (figs. 36 & 37), has the centrum broader in proportion 

 to its length and height than in Stridhio. The contour of the preaxial surface [ac] is 

 subhexagonal, with the upper line short and emarginate, forming the lower boundary of 

 the neural canal {n). 



The surface of ac is in'egular, indicative of syndesmotic union with the sacrum (or 

 first caudal), deviating on the whole from flatness by a slight convexity : the opposite 

 articular surface is undulate, slightly concave at the middle third, convex to the 

 periphery : the angles of the hexagon are rounded off. The under surface is lon- 

 gitudinally concave, a mid channel being bounded by a pair of longitudinal ridges. A 

 thick, short, obtuse, subbifid parapophysial ridge (fig. 37, ^j) extends from the middle 

 of the antero-lateral part of the centrum obliquely backward to near the upper and 

 outer angle of the hinder articular surface. The neural canal (fig. 30, n) is small and 

 subcircular ; in Struthio its section gives a vertical ellipse. The diapophysis is repre- 

 sented by the upper division (fig. 36, d) of the tuberous diparapophysis. In Struthio 

 the diapophysis is a distinct process from the parapophysis, and is the longer and larger 

 of the two. The neural canal in Struthio is surmounted by a thick subquadrate mass 

 with its enlarged tuberous extremity subbifid posteriorly. 



In Dinornis the character of the double neural spine, which distinguishes, in the 

 present comparison, several of the neck-vertebrae, is resumed in those of the tail. A 

 pair of low, thick, short, tuberous processes (fig. 36, ns) diverge from the roof of the 

 neural canal and simulate a ' sjmia bifida.' 



This character is continued through the caudal series to the foremost of the three 

 vertebrae (figs. 38, 39), which coalesce to form the homologue of the terminal 'os 



VOL. X, — PART in. No. 7. — October 1st, 1877. 2 c 



