Common Pigeon. 19 



carrying unanchylosed ribs, are much fewer and less variable in 

 number than the cervical, their number varying- from six to ten ; 

 they contrast even more strongly with the cervical in their posses- 

 sion of scarcely any mobility, some of them being ordinarily fused 

 with each other, and one or more with the ilium and sacrum. The 

 sacral vertebrae vary in number from nine to twenty, the caudal 

 from five to nine ; they resemble the cervical in being mobile, but 

 difier from it, as also from the series homologous to themselves in 

 mammals, in being the least variable in number of any of the seg- 

 ments of the vertebral column. 



The neck vertebrae of this, as of other birds, differ from those of 

 mammals in their greater number, in the conformation of the 

 articular surfaces of their centres, and in the soft tissues, cartilages, 

 and synovial capsules, with which those articular surfaces were clothed 

 in the fresh state ; in the attachment of the ligamentum nuchae 

 to the bases and not to the apices of the neural spines, a condition 

 by which, as by those previously specified, greater mobility was 

 secured for this part of the column in the bird ; and, finally, 

 by the development of hypapophyses in the anterior and posterior, 

 and of a demi-canal in the middle portion of the region along- and 

 beneath the bodies of the vertebrae. The second cervical vertebra 

 has articular processes developed upon its neural arch as well as 

 upon the odontoid process, a point in which the Bird and Reptile 

 coincide as in many others, and differ from the mammal, and 

 which throws light upon the homological nature of the odontoid. 

 The neural arches of the cervical vertebrae posterior to the second 

 are considerably emarginated in the middle line, both before and 

 behind, so that a lozenge-shaped space crossed in the natural con- 

 dition of the part from before backwards by the ligamentum 

 nuchae is left uncovered by any bony roof in the middle line of the 

 roof of the neural canal. The neural spines, or rather the central 

 depressions at the base of the most elevated portions of each neural 

 arch, to which each segment of the ligamentum nuchae is attached, 

 being situated at about the central point from before backwards in 

 each neural arch, greater length and greater range of extensibility 

 and recoil is secured for the elastic ligament. In the Pigeon the 

 four anteriorly and the two posteriorly-placed cervical vertebrae 

 are provided with hypapophyses. The six centrally-placed, which 

 make the entire complement of twelve cervical vertebrae which this 



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