34 HUMAN PHYSIOLOGY 



more oval, as if the interfibrillar substance increased in 

 amount and became of the same refractive index as the 

 fibres. During old age, a fibrillation of the homogeneous- 

 looking cartilage is brought out, especially in costal cartilage, 

 by the deposition of lime salts in the matrix, between the 

 fibres. It was long ago shown that in inflammation of 

 cartilage this fibrillation appears ; and by digesting in baryta 

 water, a similar structure may be brought out. The close 

 connection of cartilage with fibrous tissue is thus clearly 

 demonstrated. 



Such homogeneous or hyaline cartilage precedes most of 

 the bones in the embryo, and covers the ends of the long 

 bones in the adult (articular cartilage), forms the frame- 

 work of the larynx and trachea, and constitutes the costal 

 cartilages. 



(2) Elastic Fibro-Cartilage. In certain situations, a 

 specially elastic form of cartilage is developed e.g. in the 

 external ear, elastic fibres appearing in the cartilaginous 

 matrix, and forming a network through it. 



(3) 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 cartilage are found. It is also found when white 

 fibrous tissue, as tendon, is inserted into hyaline cartilage, 

 and is really a mixture of two tissues white fibrous tissue 

 and cartilage. 



4. Bone. The great supporting tissue of the adult is BONE. 



(1) DEVELOPMENT AND STRUCTURE. Bone is formed by a 

 deposition of lime salts in layers or lamellae of white fibrous 

 tissue ; but while some bones, as those of the cranial vault, 

 face, and clavicle, are produced entirely in fibrous tissue, 

 others are performed in cartilage, which acts as a scaffolding 

 upon which the formation of bone goes on. 



Intra-membranous Bone Development. This may be well 

 studied in any of the bones of the cranial vault where 

 cartilage is absent (Fig. 12). 



At the centre of ossification the matrix between the fibres 

 becomes impregnated with lime salts, chiefly the phosphate 

 and carbonate. How this deposition takes place is not 



