700 MAMMALIA. 



hare; it forms the blubber of whales. Beneath the skin 

 is a thin sheet of muscle (the panniculus carnosus), by 

 means of which the skin can be twitched, as in horses, 

 etc., and when this is removed with the skin, many of the 

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

 (see Parker's Zootomy). 



Skeleton. The bones, like 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, 

 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 (fused 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 

 ring is divided transversely by a ligament, through the 

 upper part the spinal cord passes, into the lower the odon- 

 toid process projects. The transverse processes are very 

 broad; the articular surfaces for the two condyles of the 

 skull are large and deep. 



The second vertebra or axis has a broad flat centrum 

 produced in front in the odontoid process. The neural 

 spine forms a prominent crest, the transverse processes are 

 small, the anterior articular surfaces are large. 



A typical lumbar vertebra will show the centrum and its 

 epiphyses, the neural arch and neural spine, the transverse 

 processes, the anterior and posterior articular processes or 

 zygapophyses, the median ventral hypapophysis, the small 

 anapophyses from the neural arch below the posterior 



