SEC. IV ANATOMY OF BIRDS 207 



surpassed by that of the pelvic region of the spine. Dorsal 

 vertebrae also usually differ a good deal from most cervicals in 

 having shorter bodies, laterally compressed, producing a ridge 

 which runs along their middle line below ; in lacking a vertebrar- 

 terial canal ; in having on each side two articular facets, — one on 

 the body and the other on the transverse process, for the head and 

 shoulder of a rib. They are further distinguished, usually, by 

 having large spinous processes, in the form of high, long, thin, 

 squarish plates, often or usually ankylosed together. Their trans- 

 verse processes are also very prominent laterally, thin and 

 horizontal, and often ankylosed. More or fewer dorsals may bear 

 large hypapophyses ; which, as in the loon, may bifurcate at their 

 ends into two flaring plates. Such processes continue a similar 

 series from the neck, and are in relation to the advantageous action 

 of the muscles (rectus colli anticus and longus colli) by which the neck 

 is made to straighten out from the lower curve of its sigmoid 

 flexure. 



The " Sacrum " of a Bird (Figs. 57 and 60) is commonly con- 

 sidered to be that large solid mass of numerous ankylosed vertebrse 

 in the region of the pelvis, covered in by, and fused more or less 

 completely with, the principal bones of the pelvis, or haunch-bones 

 (Uia). But in this consolidation of an extremely variable number 

 (averaging perhaps twelve, but running up to at least twenty, eleven 

 to thirteen being usual) of bones are included vertebrae which in 

 other animals belong to several different sets — dorsal, lumbar, 

 sacral proper, and coccygeal or caudal. We have just seen that one 

 or two, even three, vertebrae, which are dorsal according to the 

 definition agreed upon, may enter into the composition of the 

 "sacrum," being firmly ankylosed therewith, and their long ribs 

 issuing out from underneath the ilia, as shown in Fig. 56, sr. Next 

 comes one bone, or a series of several (two to five or more) bones, 

 ankylosed together by their bodies and spinous processes, and also 

 ankylosed with the ilia by means of stout lateral bars of bone sent 

 transversely outward on either side from their respective centra to 

 abut against the ilia. These cross-bars correspond in general form 

 and position with the transverse process of the last true rib-bearing 

 dorsal, — that process against which the shoulder of any developed 

 rib abuts ; they are variously considered to be, to represent, or to 

 include, rudimentary ribs ; and such difference of view may be war- 

 ranted by the state of the parts in different birds. However this 

 may be, the bones just described are lumbar vertebrae (Lat. lumbus, 

 the loin; where such vertebrae are situated in man and other 

 mammals); which certainly possess abortive ribs in some cases. 

 On successive lumbars the cross-bars, whatever their nature, com- 

 monly slip lower and lower downward (belly-ward) on the vertebral 



