14 DESCRIPTIONS OF PREPARATIONS. 



Cavia into the cervical region, see Plates xxiv and xxv; and for the same pro- 

 longation in Ungulata, see PI. xxix. /. c. 



For a detailed comparison of the osteological differences between tame and 

 wild Rabbits, see Darwin, History of Plants and Animals under Domestication, i. 

 pp. 120-136, 2nd ed. 1875. 



4. CERVICAL, DORSAL, LUMBAR, SACRAL, AND CAUDAL 

 VERTEBRAE OF RABBIT (Lepus cumculus). 



GREAT mobility is secured by the particular arrangements observable 

 in the region where the two upper cervical vertebrae articulate with each 

 other and with the skull, and in the region of the lower dorsal and upper 

 lumbar vertebrae. On the other hand, the transverse processes of the lower 

 cervical vertebrae and the imbricated neural spines of the upper dorsal ver- 

 tebrae prevent the possibility of any great range of movement between any 

 two of the constituent segments of those portions of the spinal column. 



The cervical vertebrae are seven in number, as almost invariably in 

 the Mammalian class ; the numbers of the dorsal and lumbar series are 

 variable, but twelve and seven, the numbers of the dorsal and lumbar ver- 

 tebrae respectively in the Rabbit, are very common numbers for those 

 series throughout the class. The number of the caudal vertebrae is the 

 most variable, that of the lumbar next, that of the dorsal less than that of 

 the lumbar, that of the cervical the least variable of these four sets of ver- 

 tebrae. As the number of the cervical vertebrae is all but invariable, the 

 variability of the length of the cervical region depends upon variations in 

 the length of the bodies of the seven vertebrae. The first cervical vertebra 

 or ' atlas ' is the widest from side to side of all the neck vertebrae ; it has a 

 low but broad neural arch, and superadded to it in front a smaller arch 

 which is in the perfect condition of the parts made into a ring for the 

 reception of the ' odontoid process ' of the next vertebra by a transverse 

 ligament. Its neural arch is overhung by the spine of that vertebra, and it 

 does not give any point of attachment to the ligamenttim nuchae. It con- 

 tains two more or less separated canals for segments of the vertebral artery ; 

 one of them pierces the base of its broad ' transverse process ' from behind 

 forwards, the other turns more or less horizontally from without, inwards, 

 behind and below the articular processes. This latter canal may be repre- 

 sented merely by a groove in the Rat, and ordinarily has this imperfect 

 character in the human subject. The former has generally a short horizontal 

 canal leading forward from it and opening on the anterior surface of the 

 transverse process ; it is however absent in the Leporidae, though present in 

 the Rat and many or most other Rodents. The second cervical or ' axis ' 

 vertebra has its spine greatly developed, both anteroposteriorly and verti- 

 cally, giving attachment by it both to the muscles which move, and the 



