350 THE TISSUES. 



its length is, however, in part compensated by the fact that the 

 peculiar attachment of the cervix femoris converts this bone (as a 

 column of support) into an arch; and thus brings its elasticity also 

 to bear on its strength. 



Development of the Bones. 



Most of the bones are developed in cartilages, which, in the aggre- 

 gate, constitute the cartilaginous skeleton (p. 316) ; the rest being 

 formed in a soft blastema. The former are sometimes termed pri- 

 mary, and the latter secondary, bones. 



The cartilages constituting the cartilaginous skeleton are deve- 

 loped like other true cartilages (p. 317), and grow in a similar man- 

 ner, till ossification commences within them ; and which extends 

 from within outwards till the whole is converted into or, more 

 accurately speaking, is replaced by bone. 



The cartilaginous skeleton, and its conversion into the various 

 bones, will first be described ; and then the development of the 

 secondary bones (the flat bones of the cranium, &c.) will be ex- 

 plained. 



It follows that the primary cartilaginous skeleton is not so complete 

 as the osseous skeleton ; but it also presents some portions which 

 either remain in a cartilaginous state, or are subsequently entirely 

 removed. It consists -first, of a complete vertebral column, with as 

 many cartilages as there are afterwards osseous vertebrae, and with 

 intervertebral ligaments; secondly, cartilaginous ribs and sternum; 

 thirdly, cartilaginous extremities with as many pieces as there are 

 subsequently bones, except that the pelvic cartilages are in a single 

 mass; and, fourthly, an incomplete cartilaginous cranium. The last 

 forms a continuous cartilaginous mass at first, and corresponds to 

 the occipital bone (except its upper half), the sphenoid (except the 

 external lamina of the pterygoid process), the mastoid and petrous 

 portions of the temporal bone, the ethmoid, the inferior turbinated 

 bone, the hyoid bone, and the ossicula auditus. The cartilaginous 

 cranium also presents the parts before alluded to, as either remain- 

 ing in a cartilaginous state, or entirely disappearing as Meckel's 

 process, two cartilaginous lamella? below the nasal bones, a narrow 

 band connecting the styloid process with the hyoid bone ; another 

 extending from the outer part of the ala parva to the lamina crib- 

 rosa; and a third reaching upwards and forwards from the carti- 

 laginous mastoid and petrous portions of the temporal bone. 



