THE SPIRAL SKELETON. 



59 



his own order, be reduced to three bones, as sometimes in the 

 Magot (limits}. 



FIG. 69. CAUDAL VERTEBRA FIG. 70 POST-AXIAL TERMINATION OF THE 

 OF Innns. VERTEBRAL COLUMN IN A SALMON. 



(Front Specimens in the British Museum.) 



It is in aquatic forms that the tail attains the greatest 

 relative bulk, and in some Sharks may contain the prodigious 

 number of 270 vertebrae. 



It is in the Tortoises that we find the tail supported by the 

 only free vertebrae which are not cervical, all those of the 

 trunk being immovably united with the ribs and with the 

 dermal bony plates forming altogether the shell, or carapace. 



The maximum of degradation and abortion of the coccyx 

 is in the Bats, where coccygeal vertebrae may be reduced to two. 



The coccyx of birds generally consists of from six to eight 

 vertebrae, but may have ten. At its end is a so-called plough- 

 share-bone, consisting of two or more anchylosed vertebras. 



The peculiar coccyx of the Frog never consists of distinct 

 vertebrae at any time of life, but is formed by the ossification 

 of the membrane which surrounds the notochord, to which 

 two small neural arches become attached. 



In osseous Fishes the end of the tail is turned up and 

 remains persistently as a cartilaginous rudiment at the end of 

 the vertebral column, generally hidden and enclosed by special 

 bony plates. 



In the higher animals provided with numerous coccygeal 

 vertebrae, these vertebras are often provided with processes 

 and articulations as complex as those of vertebrae more 

 anteriorly situate. Pre- and post-zygapophyses, anterior and 



