INTRODUCTORY. 7 



earthy matter, and tlie animal matter will remain in the 

 shape of the bone, but extremely flexible. 



In the extremely young subject all the bones are 

 cartilaginous, being elastic and pliable, but afterwards, by 

 the deposit of earthy matter in their substance and by 

 alteration in the arrangement of their component ele- 

 ments, they change to bono. This process of ossifica- 

 tion (bone makings), commencing at fixed points, involves 

 gradually the surrounding cartilage. These points are 

 termed centres of ossification. Some cartilages remain of 

 fixed structure throughout life, and are termed "|jerma- 

 7ient,^' They with the bones therefore form the skeleton, 

 which is composed of many portions brought into mov- 

 able contact with each other, whereby the various motions 

 of the body are possible and concussion from motion 

 modified, and thus shock to internal organs prevented. 

 Where firm power of support and resistance is required 

 bone is situated ; where yielding with protection to other 

 parts, cartilage. When these structures are placed in 

 position and maintained there by artificial means we have 

 an artificial skeleton, but in the natural sheleton they are 

 bound together by bands or layers of a strong glistening 

 fibrous substance (tvhite fibrous tissue) or of a yellow elastic 

 tissue, the characters of which are expressed by its name. 

 These are ligaments. The white fibrous tissue under the 

 microscope is found to be composed of collections of 

 parallel bands of wavy fibres with a single outline, which 

 bands cross each other irregularly. Yellow elastic tissue 

 consists of fibres with a double outline, which are irregu- 

 larly arranged, but send branches to the neighbouring 

 fibres, and are curled at their extremities in consequence of 

 their elastic recoil. 



Cartilage consists essentially of cells (circumscribed sacs, 

 each containing smaller sacs or nuclei, which contain a cen- 

 tral spot or nucleolus) with an ijiter cellular substance or 

 matrix. In the true or hyaline cartilage this matrix is 

 devoid of structure, being slightly granular ; but when 

 cartilage requires increased strength we find the matrix 

 assuming the characters of white fibrous tissue ; where it 

 requires elasticity, yellow elastic tissue ; thus, white fibro- 

 cartilage and yellow elastic fibro-cartilage are formed. 

 These three forms of permanent cartilage present cells 

 collected in groups of about three or four, which have been 



