412 



ZOOLOGY 



SECT. 



Song-birds. There is very commonly more or less fusion of 

 the thoracic vertebrae, and the formation of a syn-sacrum by 

 the concrescence of the posterior thoracic, lumbar, sacral, and 

 anterior caudal vertebras is universal. The posterior cervical 

 and anterior thoracic vertebras commonly bear strong hypa- 

 pophyses or inferior processes for the origin of the great flexor 

 muscles of the neck. The number of true sacral vertebras varies 

 from one to five. A pygostyle, formed by the fusion of more or 

 fewer of the caudal vertebras, is of general occurrence, but is small 

 and insignificant or absent in the Ratitas. 



FIO. 1073. Sterna of various Birds. A, Gallus (common Fowl, young) ; B, Turdus (Thrush) ; 

 C, Vultur (Vulture) ; D, Procellaria (Petrel) ; E, Casuarius (Cassowary), ant. lat. pr. 

 anterior lateral process,; car. carina ; cl. clavicle; cor. coracoid ; /on. fontanelle ; fur. 

 furcula ; obi. lat. pr. oblique lateral process ; os. paired ossification of sternum in E ; os. 1, 

 carinal ossification in A ; os. 2, os. 3, lateral ossifications ; post. med. pr. posterior median 

 process ; post. lat. pr. posterior lateral process ; pr. cor. pro-coracoid ; scp. scapula ; sp. 

 spina sterni. (A and E, after W. K. Parker ; B, C, and D, from Bronn's Thierreich.) 



The ribs are always double-headed, the sternal ribs are ossified, 

 not merely calcified, and are united with the vertebral ribs by 

 synovial joints. Ossified uncinates are nearly always present, and 

 usually become ankylosed to the vertebral ribs. 



What may be considered as the normal type of sternum is a 

 broad plate, concave dorsally from side to side, and produced 

 ventrally into an antero-posterior keel which is ossified from a 

 distinct centre (Fig. 1073, A, os. 1). The posterior edge of the bone 

 is either entire (D), or presents on each side of the keel one or two 



