OF THE GREAT AUK, OR GARFOWL. 321 
In the eighth dorsal, the hypapophysis is suddenly reduced to a low triangular process. 
The pleurapophysis, 6 inches 3 lines in length, articulates with a hemapophysis of more 
slender proportions, 5 inches 2 lines in length. 
In the ninth dorsal, the hypapophysis is again represented by a low median ridge. 
The pleurapophysis, 6 inches 6 lines in length, articulates with a hemapopbysis (h) 
5 inches 6 lines in length; and this is the last of those that directly articulate with the 
sternum. 
The tenth dorsal becomes, by confluence of its centrum, the first sacral (ib. s), but 
retains its neural spine distinct from, though contiguous with, the long sacral ridge ; its 
pleurapophysis (pl) is 6 inches 2 lines in length, and articulates with a hemapophysis (h) 
5 inches 2 lines in length, the distal end of which is applied to the preceding hemapo- 
physis about one inch from its articular end. 
In the dorsal region, the articular facets of the centrum are simplified to a very slight 
convexity in front and a corresponding concavity behind (Pl. LII. fig. 7, c). 
The sacrum (Pl. LI. fig. 1, s), 4 inches 2 lines in length, and including about thirteen 
vertebrz, presents at its beginning rather long and narrow centrums; but these expand 
laterally, and subside vertically to the sixth, whence they gradually again contract in 
breadth to the antepenultimate vertebra: the centrums are all confluent. The hinder 
half of the expanded rhomboid portion of the under surface of the sacrum is broadly 
and slightly grooved. 
Transverse processes, from the second to the sixth sacral inclusive, abut against the 
ilia: in the next three vertebra these processes are scarcely marked ; they reappear in 
the following sacrals, with articular surfaces for the ilia, increasing in vertical extent. 
The first free caudal has also a short thick transverse process, which abuts-against the 
ilio-ischial part of the os innominatum. 
The length of the iliac element (PI. LI. fig. 1, 62) of this bone is 4 inches 6 lines ; its 
extreme breadth, an inch from the fore margin, is 9 lines. That margin is rounded ; 
the outer one is at first convex, then concave, contracting before expanding again, and 
thickening (at 62) to contribute to the acetabulum. The expanded fore part of the 
ilium is a very thin lamella. The acetabulum, widely open, is overtopped by an articular 
facet adapted to the upper part of the neck of the femur. The ilium quickly contracts 
in breadth behind the acetabulum, beyond which it extends nearly 2 inches, as far back as 
the third caudal; it coalesces with the ischium about an inch behind the acetabulum, cir- 
cumscribing an elliptic ischiadic foramen (7) 9 lines in length and 4 lines in short diameter. 
The ischium (63), after the iliac confluence, extends backward as a pointed styloid 
process an inch in length. The ischium forms the back part of the acetabulum, the 
pubis the under part; the obturator vacuity (0) between ischium and pubis is only 
5 lines in length and 2 lines in short diameter. The ischio-pubic harmonia beyond this 
is 1} inch in length ; the slender pubis (61) then extends freely backward and slightly out- 
ward and downward for 2 inches 6 lines, of a rib-like shape ; its total length is 4 inches. 
