SPINAL COLUMN OF BIRDS. 365 



with the tympanic bone. The articulation of the head with the 

 vertebral column permits more varied movement than in the 

 Mammalia ; for it is effected by a single condyle, a kind of half- 

 spherical pivot, situated on the central line of the body, below 

 the large occipital foramen, and received into a corresponding 

 cavity in the atlas. 



327. The neck of Birds is generally longer and more move^ 

 able than that of most Mammalia ; as the beak is generally the 

 only organ of prehension by which they pick up their food from 

 the ground, the cervical portion of the vertebral column (Fig. 

 J 77) becomes longer, in proportion as these animals are more 

 elevated on their feet ; and where they are essentially swimmers, 

 as the Swan, and plunge their head in the water to seize their 

 prey, the length of their neck in many cases much surpasses the 

 height of the trunk. The number of cervical vertebra varies 

 in different species ; generally there are from twelve to fifteen, 

 but in some cases there are not so many, and in others there are 

 more than twenty, as in the Swan for instance. They move 

 easily on one another, and from the nature of their articulating 

 surfaces, the neck can bend in the form of an S, so as to shorten 

 or lengthen, as the curves increase or diminish. This arrangement 

 is particularly remarkable in Waders, such as the Stork ; which, 

 to seize their prey, require to dart their beak to a considerable 

 distance with great rapidity. The action of the muscles destined 

 to move this part, is also facilitated by the existence of numerous 

 processes, serving for their insertion. The vertebra of the 

 back, on the contrary, are in nearly all Birds, almost immovable ; 

 and we readily perceive the importance of this arrangement in 

 animals destined for flight ; for this portion of the spinal column, 

 serving to support the ribs, and consequently furnishing a point 

 of attachment to the wings, requires great solidity. In general 

 these vertebrae are even united to each other; but in Birds 

 which do not fly, such as the Cassowary and the Ostrich, they 

 preserve some power of motion. The lumbar and sacral vertebra 

 are all united in a single bone, which has the same use as the 

 sacrum in Man. The coccygeal vertebrae are small and move- 

 able ; the last, which supports the large feathers of the tail, is 



