CONNECTIVE TISSUES 



45 



(2) Elastic Fibro-Cartilage. — In certain situations — e.g. in 

 the external ear — a specially elastic form of cartilage is 

 developed, elastic fibres appearing in the cartilaginous 

 matrix, and forming- a network through it. 



(o) White Fibro-Cartilage. — In other situations — e.g. the 

 intervertebral discs — a combination of the binding action of 

 fibrous tissue with the padding action of cartilage is required ; 

 and here strands of white 

 fibrous tissue with little 

 islands of hyaline cartil- 

 age are found. It is also 

 found where white fibrous 

 tissue, e.g. tendon, is in- 

 serted into hyaline cartil- 

 age, and it is reall}^ a 

 mixture of two tissues — 

 wdiite fibrous tissue and 



cartilage. 



great 



4. Bone. — The 

 supporting tissue of the 

 adult is Bone. 



(1) Development and 

 Structure. — Bone is 

 formed by a deposition of 

 lime salts in layers or 

 lainellcB of white fibrous 

 tissue. But while some 

 bones, as those of the 

 cranial vault, face, and 



Fig. 13. — Intra-membranous Bone De- 

 velopment in the lower jaw of a fcetal 

 cat. Above, the process of ossification 

 is seen shooting out along the fibres, 

 and on the lower surface the process 

 of absorption is going on. Two osteo- 

 clasts — large multi-nucleated cells — 

 are shown to the left. 



clavicle, are produced entirely in fibrous tissue, others are 

 preformed in cartilage, which acts as a scaffolding upon 

 which the formation of bone goes on. 



A. Intra-membranous Bone Development. — This may be 

 studied in any of the bones of the cranial vault where 

 cartilage is absent (fig. 13). 



At the centre of ossification, the matrix between the 

 fibres becomes impregnated with lime salts, chiefly the phos- 

 phate and carbonate. How this deposition takes place is 



