AND DEVELOPMENT OF BONE. 203 



very widely different, and it is to be regretted that distinctive names 

 should not have been assigned to each. The simplest lorm of car- 

 tilage, spoken of as permanent cartilage, is met with in the external 

 ear, the nose and the eyelids, &e. It is remarkable for flexibility and 

 preservation of form. This property of permanent cartilage admir- 

 ably adapts it for maintaining the identity of the features of the indi- 

 vidual throughout life. In ultimate structure it is one of the most 

 simple of the living tissues. A slight modification of this form of 

 cartilage is applied to the investment of the extremities of the long 

 bones, and also for the covering of those portions of bones which, in 

 other situations than the joints, are subject to attrition, thus the ten- 

 dons of many muscles play in bony grooves, such grooves being lined 

 with this form of articular cartilage. These forms of cartilage are 

 spoken of as permanent cartilage and are not prone to ossify, their 

 ossification when it does take place being due to pathological* change, 

 and not to the development of a physiological property. But, under the 

 name of temporary cartilage, we have to make ourselves acquainted 

 with a tissue whose intimate structure is widely different from that of 

 which we have just spoken, and whose physiological function is to 

 serve as a nidus for the development of bone. It differs from permanent 

 cartilage, inasmuch as the cells which enter into its composition are 

 not irregularly dispersed through the surrounding fibrous tissue, but 

 are so disposed as to assume a linear direction, corresponding with the 

 axis of the bone undergoing development. Moreover, the fibres con- 

 stituting the fibrous tissue have a similar direction. We have already 

 seen, that white fibrous tissue is especially prone to ossification, as ex- 

 emplified in the case of the tendons of the legs of many birds. The 

 fibrous tissue of the cartilage is the especial seat of ossification, the 

 cells leaving interspaces constituting the cancellated structure of bone. 



The axial extremities of bones being covered with cartilage, and the 

 fibrous element of this cartilage being the seat of the osteogenetic 

 power, it is manifest that the increase in the length of a bone is 

 effected by addition to its extremities. 



Another question, however, arises as to whether a long bone in- 

 creases in length equally at both extremities. John Hunter, Duha- 

 mel and Flourens, had previously made numerous experiments in re- 

 ference to this subject ; more lately Oilier has devoted himself to 

 the enquiry. Without entering into all the details of his experiments, 

 made upon rabbits, it will suffice to say that in the case of the humerus 



