4 MR. ST. GEORGE MIVART ON THE 
of the pleural lamella; and the interzygapophysial ridge may be very conspicuously 
perforated. 
The third vertebra is again relatively shorter and higher than in Séruthio. Both 
articular central surfaces look more dorsad and ventrad respectively; and the lateral 
margins of the postaxial one are not, or but very slightly, concave. The hypapophysis 
extends more postaxiad; but the neural spine does not extend so much preaxiad as in 
Struthio. The postzygapophyses look entirely ventrad. The hyperapophyses are as 
large as in the axis and are grooved pre- and postaxially. The neural spine does not 
rise suddenly preaxially, and is hardly at all preaxially excavated. The interzygapo- 
physial ridge is perforated, but not so conspicuously as in the axis. 
FOURTH VERTEBRA OF RHEA (natural size). 
Fig. 5. 

Dorsal view. Letters as before. 
The fourth vertebra is again much shorter relatively as well as absolutely than in 
Struthio, is more equal in length to the third, and more quadrate when viewed dorsally, 
its transverse diameters between the pree- and between the postzygapophyses being sub- 
equal. The neural spine is slightly excavated preaxially, but is deeply so postaxially. 
The fifth vertebra.—The contrast as to length between this and the preceding ver- 
tebra in Rhea is something like that existing between the third and fourth vertebra in 
Struthio. The neural arch is not more cut away preaxially than in the fourth vertebra. 
There is no hypapophysis, and hardly a trace of hyperapophyses. The neural spine (like 
that of Struthio’s fourth vertebra) is reduced in size, and is slightly and subequally 
excavated at both ends. ‘The transverse diameter of the preaxial part of the vertebra 
(viewed dorsally) decidedly exceeds that of its postaxial end. 
The siath vertebra is much longer and more slender, and differs from the fifth much 
more than does the fifth from the fourth, the increase in length thus taking place later 
in the vertebral series in Rhea than in Struthio. The styliform ribs are very much 
shorter; but, as in Struthio, the catapophyses are first marked in this vertebra. The 
