18 ANATOMY OF VERTEBRATES. 



compressed quadrate plate, its truncate summit is often thickened, 

 sometimes produced forward and backward to fix the vertebra? 

 from their highest points ; ossified tendons of spinal muscles, also, 

 aid the coalesced spinous and transverse processes in fixing part of 

 the dorsal region, but only in birds of powerful flight, and not in 

 all such. The partial anchylosis of the dorsal region is associated 

 in Falcons with their ' hovering ' action. The pleurapophyses 

 or ' vertebral ribs ' articulate moveably to the dorsal vertebras, as 

 also to the anterior sacral, Avhen developed there to form part of 

 the compages of the ' chest.' In the first, and usually the second 

 dorsal, they are free, pointed, floating ribs, fig. 12, i, 2, fig. 13, pi ; 

 they articulate with bony ' hasmapophyses ' or ' sternal ribs,'ib.,/i, 

 d^ in the remaining dorsals. As the vertebral ribs are placed more 

 backward, the neck or pedicle supporting the head elongates, and 

 this articulates with the parapophysial surface or tubercle, close 

 to the anterior border of the centrum ; rarely, as in the Penguin ^ 

 and Ostrich, encroaching upon the intervertebral space. The 

 tubercle of the rib is, in most, supported on an elongate compressed 

 base, and articulates by a synovial joint with the diapophysis. 

 The body of the rib, where formed by the union of the two arti- 

 cular processes, is compressed, or tliin from side to side, but broad 

 from within outward; but the outer margin soon expands both 

 forward and backward beyond the compressed part of the body of 

 the rib ; this part, as the rib extends down, subsides, the outer 

 margin maintaining or increasing its breadth, and forming the rest 

 of the rib, giving to it a flattened surface externally. This is the 

 common but not constant character of the dorsal pleurapophyses. 

 These ribs are broadest in proportion to their length in the 

 ^/>^^r?/x,^ narrowest and also longest in the Guillemots and Auks^; 

 they are slender in most Lisessores ; broad and strong in Raj)tores. 

 The second, third, and fourth ribs are partially and remarkably 

 expanded in Wood-peckers. In all birds the end of the vertebral 

 rib articulatino; with a sternal one is thickened to form the sub- 

 convex surface of the synovial joint. There may be several mi- 

 nute pneumatic foramina, but the most constant and conspicuous 

 is below the tubercle. 



An ' epipleural ' appendage, fig. 12, «, is attached to most, if not 

 all, the moveable pleurapophyses between the first and last, and 

 consequently may be found in the pair of which the centrum has 

 become part of the sacrum. These appendages are oblong flat 

 bones, varying in tlie proportions of length and breadth in dif- 

 ferent species, and also in their mode of union to their rib : they 

 ' X-. pi. 52, fig. 48. 2 xr. pi. 54. ^ xii-. 



