THE SKELETON. 29 



and an ischiac ono in Rhea., but in all other birds the pelvis is open below, and 

 the pubic l)ones, as a rule, project jjosteriorly as more or less slender styles. 

 In the postacetabular region the under side of the pelvis exhibits more or less 

 of an excavation or concavity, the bones being fashioned to produce this as a 

 receptacle and a protection to the contained viscera. This jielvic basin is 

 ample and spacious in others (Grebes). An ncctahnJum is always perforated 

 at its base; it is the cup in which the head of the femur or thigh bone of the 

 leg articulates, and above it we find an antitrochanter for articulation with 

 the same bone. In Gcococcyx, the fowls, and some other birds, the pubic 

 bone is produced a little way in front of the acetabulum as &propuhis or pro- 

 pubic process. 



The skeleton of the tail of all recent birds is composed of a few, 

 but a varying number, of caudal vcrti-hrw, and a terminal piece, called 

 the ploughshare bone, coccyx, or the pygostyle, it tcjo being composed of a 

 number of caudal vertebrae fused together into one piece. All of the caudal 

 segments, apart from the pygostyle, are more or less rudimentary in character, 

 becoming more and more so as we proceed posteriorly. Still, as in all true 

 vertebrae, they possess a centrum, a neural canal, and tranverse processes. A 

 few of the ultimate ones, however, in some forms, may even lack those charac- 

 ters. As the pelvic arch or "pelvic girdle" is the bone to which the pelvic 

 limbs are articulated, so it is, at the anterior moiety of the body, we find the 

 jyectoral arch or shoulder girdle to which the skeleton of the wings are articu- 

 lated. 



Commonly in birds this is composed of five bones, that is, a pair of 

 scapulae, a pair of coracoids and the furerdwn or furcula. This latter U or V 

 shaped arch is popularly known as the "wish-bone" or "merry thought" and 

 is in reality the united clavicles, so in point of fact the shoulder-girdle is com- 

 posed of six, or three pairs of bones. The furcula may be more or less rudi- 

 mentary or even entirely absent. On either side above, its free end usually 

 articulates with both coracoid and scapula, while below, in the median line, it 

 often supports a well developed process, the hypocleidium. Occasionally, as 

 in certain Swans, it is modified in form at its lower part by the windpipe or 

 trachea. 



In Ducks and many other birds the furcula is solid, while in Vultures and 

 numerous others it in pneumatic, that is, air gains access to its interior through 

 pneumatic foramina. In some birds the entire skeleton enjoys this condition 

 {^Catharisfa, for example) while in others, as the Penguins, it is almost entirely 

 absent. 



Each si-apnla is a long and cimeter-shaped bone, exhibiting a head, neck, 

 and blade. The head developes a glenoid process which assists in forming the 

 glenoid cavity for articulation with the head of the humerus, and an acromial 



