423 
In Apteryx australis there are nine caudal vertebrae, the anterior ones of greater 
relative vertical extent than in Struthionide; 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 (3 nat. size). 
Fig. 36. Fig. 37. 

Aspects, 
Fig. 36, preaxial; 37, lateral. 
Iam not certain that I possess the fortieth vertebra or ‘ first free candal’ in Dinornis. 
The second, if it be not the first (figs. 86 & 37), has the centrum broader in proportion 
to its length and height than in Struthio. The contour of the preaxial surface (ac) is 
subhexagonal, with the upper line short and emarginate, forming the lower boundary ot 
the neural canal (7). 
The surface of ac is irregular, 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, p) 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. 36, 2) 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 Séruthio 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-vertebra, is resumed in those of the tail. A 
pair of low, thick, short, tuberous processes (fig. 36, ms) diverge from the roof of the 
neural canal and simulate a ‘ spina bifida.’ 
This character is continued through the caudal series to the foremost of the three 
1 Ante, p. 32, Plate VIII. 
