FORMATION OF THE TISSUES BONE. 481 



the interior of a permanent Cartilage (except when it has become vascular by 

 disease, or undergoes ossification), through the whole of life ; and there seems 

 ground to believe that, when it nas been injured by disease or accident, the 

 loss of substance is not repaired by real cartilaginous tissue. On the other 

 hand, the softer tissues of the Eye are capable of complete regeneration. 

 Every oculist is aware that a great loss of Vitreous humour may take place with- 

 out permanent injury ; and it has been found that even the Crystalline lens may 

 be completely regenerated, after it has been entirely removed by extraction. 



629. Proceeding now to the Vascular tissues, in which the processes of 

 interstitial absorption and renewal are continually taking place, we commence 

 with Bone, as the one which has the most evident relations to those already 

 described. All true Bony structure* is formed upon a basis of Cartilage ; but 

 upon the mode of transformation of one tissue into the other, additional infor- 

 mation is still much required. We shall first inquire into the characteristic 

 structure of Bone, and then into its origin. When examined with the naked 

 eye, it is seen that the bone possesses, in some degree, a laminated texture ; in 

 the long bones, the external and internal laminae are arranged concentrically 

 around the medullary canal ; and in the flat bones, they are parallel to the 

 surface. Towards the extremities of the long bones, and between the external 

 plates of the flat bones, are a number of cancelli, or small hollows bounded by 

 very thin plates of bone ; these communicate with the medullary canal where 

 it exists ; having, like it, an extremely vascular lining membrane ; and their 

 cavities being filled with a peculiar adipose matter. The hard substance of 



Tig. 113. 



The minute structure of Bone, drawn with the microscope frm nature, by Bagg magnified 300 diame- 

 ters ; 1, one of the Haversian canals surrounded by its concentric lamellae ; the corpuscles are seen 

 between the lamellae; but the converging tubuli are omitted; 2, an Haversian canal with its concentric 

 lamellae, Purkinjean corpuscles and converging tubuli ; 3, the area of one of the canals; 4, 4, direction of 

 the lamellae of the great medullary canal. Between the lamellae, at the upper part of the figure, several 

 very long corpuscles with their tubuli are seen. In the lower part of the figure, the outlines of three other 

 canals are given, in order to show their form and mode of arrangement in the entire bone. (After Wilson.) 



* The white patches formed by the deposition of earthy matter in the dura mater, in 

 the coats of the arteries, and in similar parts, cannot be so considered. It appears from 

 the researches of Mr. Smee (Med. Gaz., Nov. 1840), that the true bony structure is to be 

 met with in callus, exostoses, ossified cartilages, and other similar products, having a 

 near relation to bone ; but not in the calcareous deposits in the coats of arteries, serous 

 or fibrous membranes, or abnormal growths such as fibrous tumours of the uterus. 

 41 



