SHUFELDT.] OSTEOLOGY OF THE SPEOTYTO. 609 
pressed from side to side; the ilia which form their outer boundaries are 
convex; the neuro-spinal crest forms the roof, the basal surface being 
deficient, formed merely by the spine-like di- and par-apophyses of the 
vertebrie and the confluent neural arches. This first vertebra occupies 
the lowest level, the bird supposed to be standing asin Pl. I. Now, a 
line drawn mesial on the centra below, from the first centrum to the last 
gradually rises until opposite the anterior borders of the ischiadic fora- 
mina, then curves rather abruptly downwards to its termination. The 
centra of the first two or three vertebra are compressed from side to side 
to such an extent as to cause them to appear wedge-shaped, the common * 
apex or edge being below; after that, however, they rapidly broaden, 
become compressed vertically and more cellular in structure; they are 
very broad from the fourth to the ninth, inclusive—then as rapidly be- 
come contracted as they approach the coccyx. Minute but numerous 
pneumatic foramina are seen at or near the usual localities. The largest 
foramina for the exit of the roots of any pair of sacral nerves is gen- 
erally in the fifth vertebra; they decrease in size as they leave them 
either way. Inthe young, only the last few of these foramina are double; 
they are all double in the adult and placed one above another, a pair on 
the side of each centrum at their posterior borders, for the exit of the roots 
of the sacral nerves. The diapophyses of the anterior five sacral verte- 
bre are thrown out against the internal surfaces of the ilia, to which 
they are firmly attached, and act as braces to hold the engaged bones 
together. The parapophyses of the first, form facets for articulation 
with the sacral ribs; the second and third have none; in the fourth and 
fifth they also act as braces in the manner above described, joining the 
ilia just before their divergence commences. Reliance seems to have 
been placed entirely in the completeness of the sacro-iliac union in the 
last vertebre, for the apophysial struts terminate in that portion of the 
pelvic vault formed by the sacrum itself, except in the last two verte- 
bree, where the parapophyses abut against the iliac borders. The para- 
pophyses of that vertebra which is opposite the acetabula are promi- 
nent, they being long and ample, reaching to the border and re-enforcing 
that part of the pelvis that requires it the most, the vicinity of the 
leverage for the pelvic limbs. In other Strigide several apophyses are 
thrown out at this point. The posterior opening of the neural canal in 
the last sacral vertebra is subcircular, its diameters being about a milli- 
metre in length. This vertebra also possesses small postzygapophyses, 
looking upwards and outwards for articulation with the prezygapophyses 
of the first coccygeal vertebra; the articulating facet of the centrum is 
also small, long transversely, notched in the median line, the surface on 
either side being convex. At every point where the sacrum meets the 
iliac bones union is firm and complete, though both upon the internal 
and external surfaces the sutural traces are permanently apparent. 
The anterior iliac margins, as they diverge from the sacral spine, form an 
acute angle, concave forwards; they have a well-marked rim or border, 
nearly a millimetre in width, raised above the general surface of the 
bone, which disappears on the outer bordersas we follow them backwards. 
The two anterior and outer angles overhang the sacral and fifth or 
last dorsal pleurapophyses. From these last the marginal boundaries, 
which necessarily give the bones their form, are produced backwards and 
outwards to a point opposite the centrum of the third sacral vertebra, 
then backwards and inwards, forming at the above points two lateral 
angles. From the apices of the two lateral angles to where the borders 
terminate on either side in front of the acetabula with the pubic bones, 
the direction is such as to form a concavity on each side; the line joining 
39 H 
