PROFESSOR OWEN ON THE GENUS DINORNIS. 177 
caudal series of vertebra, of which five have been enlisted or conscripted into the 
service of the sacrum. 
The sacro-neural canal (Plate XXXI. fig. 2) retains a vertical diameter of 8 lines 
along the first three vertebre; it then expands gradually to the sixth and rapidly to 
the ninth sacral, where the vertical diameter reaches to 1 inch 6 lines. The anterior or 
‘hemal’ myelonal columns would seem to have made a bulge between the eighth 
and tenth vertebre; and the neural canal, again contracting, shows its diameter of 
8 lines between the thirteenth and fourteenth outlets, and is reduced to 4 lines in 
the last or seventeenth sacral vertebra. 
The motory and sensory divisions of the nerve-outlets continue distinct to the outer 
surface of the vertebra as far as the twelfth, the neural (dorsal, upper) or sensory 
division being the smallest, and diminishing more rapidly than the hemal (lower, 
motory) outlet after the ninth of these. The canal gains in transverse as in vertical 
expanse, but in a rather less degree. 
Parapophysial abutments cease after the eighth sacral, and are resumed at the 
twelfth. The diapophysial ones increase in length from the fifth sacral, but with 
much diminished breadth, to the ninth sacral, when they increase in breadth as well 
as length, and curve upward, backward, and _ slightly outward to buttress up the 
expanded postacetabular part of the ilium. 
Between the smooth compact inner layer of bone forming the neural canal and the 
somewhat thicker outer layer, the osseous substance of the sacrum is coarsely reticulate 
and pneumatic. Larger subserial vacuities mark, in vertical section (Plate XXXI. 
fig. 2), some of the anterior obliterated vertebral interspaces; and the longest or chief 
lamin, rising from the roof of the neural canal, indicate the neural spines at distances 
corresponding to the nerve-outlets, answering to the fourth sacral vertebra. The 
spine-plate curves gently forward; while those of the sixth, seventh, and eighth sacrals 
rise vertically, and the succeeding ones curve gently backward. 
In the comparison of the sacrum of Dinornis, as exemplified by the present spines, 
with that of Struthio, as illustrated in Prof. Mivart’s paper!, I may premise that the 
first three (anchylosed) vertebre are reckoned, by its author, as ‘dorso-lumbar’ (26th 
and 27th) and lumbar (28th) vertebre. It will be understood, therefore, that in my 
description of the specimen “in the Museum of the College of Surgeons”, figured 
in Mivart’s cut 59, “ the neural arch of the fifth sacral vertebra has advanced, 
and rests over the interspace between its own and the preceding centrum; at the 
eleventh vertebra it has resumed its normal position and connexions.” My ‘fifth sacral’ 
is Mivart’s ‘second’ (s 2), and my ‘eleventh’ sacral is Mivart’s eighth; the last five 
sacrals in the twenty anchylosed vertebre of the mature Ostrich ® are reckoned by him 
as the first five caudals in that bird. 
1 Loc. cit. pp. 420-427, figs. 58-62. * « Catalogue’ ut supra, 4to, 1853, p. 266. 
* Trans. Zool, Soc. vol. iii. pl. 19. fig. 4. 
