SKELETON OF RABBIT 787 



muscles of head and neck, limbs and trunk, are disclosed 

 (see Parker's Zootomy). 



Skeleton. — The bones, Uke those of other Vertebrates, 

 are developed either as replacements of pre-existent cartil- 

 ages, or independent of any such preformations, but in all 

 cases through the agency of active periosteal membranes. 

 By themselves, however, must be ranked little sesamoid 

 bones, which are developed within tendons and near joints, 

 notably, for instance, the patella or knee-pan. There is no 

 bony exoskeleton in any mammals except the armadillos, 



CCV. 



Fig. 470. — Front view of Mammalian atlas. 



N.C., Neural canal, crossed by a ligament (L.), above which lies 

 the spinal cord, while the odontoid process of the axis pro- 

 trudes beneath. CCV., Deep concavities for the two condyles 

 of the skull ; not much of the centrum is left ; part of it has 

 become the odontoid process. T.P., Large transverse process ; 

 N., a slight indication of the much-reduced neural spine ; the 

 reduction allows more freedom of movement to the skull. 



unless we rank the teeth, which develop in connection with 

 the skin of the jaws, as in a sense exoskeletal. 



The vertebrae may be grouped in five sets : — cervical 

 (seven in number), thoracic (with well-developed ribs), 

 lumbar (without ribs), sacral (fuseld to support the pelvis), 

 and caudal. The faces of the centra are more or less flat, 

 and between adjacent vertebrae there are intervertebral 

 discs of fibro-cartilage. A vestige of the notochord is found 

 in Mammals in the gelatinous nucleus pulposus in the centre 

 of the intervertebral discs. 



The first vertebra or atlas is ring-like, its neural canal 

 being very large, its centrum unrepresented except by the 

 odontoid process, which fuses to the second vertebra. The 



