28 GENERAL HISTORY OF BIRDS. 



ment seen in the cervicals. More or fewer of them connect Avith the sternum 

 through the intervention of the sternal or costal ribs. 



The thoracic and lumbar regions of the vertebral column are not defined 

 as in the mammals, since the dorsal vertebra support ribs, and the lumbar 

 ones fall beneath the pelvic bones and enter into the formation of the pelvic 

 sacrum. In any bird the number of cervical vertebrsB always exceed those 

 found in the dorsal region. In the cervical division of the column there may 

 be as few as nine or as many as twenty-one as in the Swan (Olor). Geococcyx 

 has but four dorsal vertebra;, which is about the minimum number. The 

 thoracic ribs may or may not support unciform processes midway upon 

 their posterior borders, though it is the rarest exception that they do not 

 [Palamedea.) These processes may or may not anchylose with the ribs that 

 possess them. 



In the vast majority of species of birds the sternum is a large bone, 

 and in the adult completely ossified. Vertically and below it develops in the 

 median plane, in most birds, a strong carina or keel for the attachment of the 

 pectoral and other muscles, and for the protection of the internal organs of 

 the thorax and upper part of the abdomen over which it extends. Those of 

 the class lacking in the power of flight, as ostrich forms, owl-parrot and a few 

 others, have keelless sterna, but in all other forms it is more or less developed. 

 Posteriorly its border may be entire and without fenestra, or it may be more 

 or less profoundly cleft once or twice, but no more, upon either side of the 

 carina, or it may be variously fenestrated in that region The costal borders 

 bear facets for the costal or sternal ribs {hfemapophyses). Anteriorly it is 

 transversely grooved to articulate with the coracoids, and it may or may not 

 possess a manubrial process in front. In Opisthocomus and a few other 

 birds, the clavicles meet the manubrium to anchylose with it, while in others 

 we find the contact very intimate, but coossification rarely takes place. 



When birds come to be fully adult, the three bones {jMum, ischium, and 

 pubis) fuse thoroughly together, and the two halves of Ihe p>elv is thus formed 

 unite with more or less closeness with the interdorsocaudal vertebras and 

 thus form the compound bone called the sacrum. The vertebral part of 

 this consists of more or fewer presacral vertebrae, two sacral vertebrae, and a 

 series of postsacrals, all firmly anchylosed together. The sacrals, correspond- 

 ing to the sacrals in the Lacertilia, are situated between the pelvic acetabula, 

 giving unusual strength in that region where the pelvic limbs are articulated. 

 Some of the presacral vertebrse may support true ribs (dorsals), and in a few 

 instances these may connect with the sternum by means of costal ribs. 



Examples of broad pelves are seen among the fowls (grouse, etc.), while 

 extremely long and laterally compressed ones are found among such divers as 

 the loons and grebes. In the ostrich {Stntthio) there is a pubic symphysis, 



