VERTEBRATA. 23 



movable, and in many species of the dorsal and caudal portions 

 admit of no motion at all. This fixity facilitates the flight of the 

 bird, whilst the length and mobility of the cervical portion of the 

 spine compensate, in some degree, for the unfitness of the anterior 

 members to the purposes of prehension, &c. 



The cervical portion of the spine is generally composed of a greater 

 number of vertebrae than any of the other divisions ; they are not 

 fewer than nine, as observed in the sparrow, nor more than twenty- 

 three, as in the swan. 



The bodies lock into each other, and are so disposed as to allow 

 the superior and inferior ones to move forwards, and the middle 

 backwards. The transverse processes are long, and have rudi- 

 mentary ribs connected to them ; these are particularly well deve- 

 loped in rapacious birds, and hence the great breadth of their necks. 

 The atlas is a simple ring, generally articulated to the occipital 

 tubercle by a single facet; but the penguin and ostrich have two 

 other facets continuous with the central one. From the dentata 

 down, a movable inter-articular cartilage is found, as in the joint of 

 the lower jaw of the mammalia. 



The dorsal vertebrae range from six in the bull-finch to eleven as 

 seen in the swan. The bodies of these vertebrae are short and 

 compressed laterally, except in the ostrich. The transverse pro- 

 cesses are greatly developed. The anterior cartilaginous surface is 

 convex in the vertical direction, concave in the transverse, and 

 connected by fibrous capsules and synovial membranes. Most 

 birds have the middle and lower vertebrae anchylosed ; even the 

 transverse and spinous processes of the superior are anchylosed in 

 those birds requiring great fixation of the trunk ; while in those that 

 cannot fly, as the penguins, they are all movable. 



The sacral vertebrae are firmly anchylosed with one another, 

 and with the ilia laterally; consequently it is difficult to determine 

 their real number ; it is not, however, greater than nineteen, as 

 seen in the emeu and cassowary, nor less ihan eight, as observed in 

 the hoopoe. The bodies of these vertebrae are broad, but shallow, 

 and the canal greatly enlarged, to correspond to the size of the 

 chord, which here supplies nerves to the posterior extremities. 

 When it is considered that the head, posterior members, viscera, &c, 

 are suspended in flight from this central portion of the trunk, the 

 necessity for the mechanism consolidating these vertebrae will be 

 readily appreciated. 



The coccygeal vertebrae are generally movable, and from five 

 to nine in number. With the exception of the last, they are broad, 

 short, and perforated for the spinal marrow. The last has no pro- 

 cesses ; it is compressed laterally, and terminates above and below 

 in a sharp edge ; it supports the coccygeal oil-gland, and affords a 

 firm basis to the tail feathers, or retrices of Linnaeus. These bones 

 possess ligamentous connections, except the sixth and seventh which 

 re provided with a capsule and synovial fluid. 



