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 haemapophysis 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 hsemapophysis {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 (pi) is 6 inches 2 lines in length, and articulates with a haeraapophysis (ft) 

 5 inches 2 lines in length, the distal end of which is applied to the preceding hsemapo- 

 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 (PI. LI. fig. 1, s), 4 inches 2 hnes in length, and including about thirteen 

 vertebrae, 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 vertebrae 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 (i) 9 lines in length and 4 lines in short diameter. 



The ischium (ea), 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 (64) 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. 



