46 HAND-BOOK OF PHYSIOLOGY. 



means of the minute streams of fluid nutrient matter which occupy the 

 canaliculi. 



It will be seen from the above description that bone is essentially con- 

 nective-tissue impregnated with lime salts: it bears a very close resem- 

 blance to what may be termed typical connective-tissue such as the 

 substance of the cornea. The bone-corpuscles with tTieir processes, occu- 

 pying the lacunae and canaliculi, correspond exactly to the cornea-cor- 

 puscles lying in branched spaces; while the finely fibrillated structure of 

 the bone-lamellae, to be presently described, resembles the fibrillated sub- 

 stance of the cornea in which the branching spaces lie. 



Lamellae of Compact Bone. In the shaft of a long bone three 

 distinct sets of lamellae can be clearly recognized. 



(1.) General or fundamental lamellae; which are most easily traceable 

 just beneath the periosteum, and around the medullary cavity, forming 

 around the latter a series of concentric rings. At a little distance from 

 the medullary and periosteal surfaces (in the deeper portions of the bone) 

 they are more or less interrupted by 



(2.) Special or Haversian lamellae, which are concentrically arranged 

 around the Haversian canals to the number of six to eighteen around 

 each. 



(3.) Interstitial lamellae, which connect the systems of Haversian 

 lamellae, filling the spaces between them, and consequently attaining 

 their greatest development where the Haversian 

 systems are few, and vice versa. 



The ultimate structure of the lamellce appears 

 to be reticular. If a thin film be peeled off the 

 surface of a bone, from which the earthy matter has 

 been removed by acid, and examined with a high 

 power of the microscope, it will be found com- 

 posed of a finely reticular structure, formed appar- 

 ently of very slender fibres decussating obliquely, 

 but coalescing at the points of intersection, as if 

 here the fibres were fused rather than woven 



Fio. 48. Thin layer peeled ,, /T -v . m /0 , x 



off from a softened bone, together (Fig. 48). (Sharpey.) 

 This figure, which is intend- T -, ,-, j_- -i i n 



ed to represent the reticular In many places these reticular lamellae are 

 perforated by tapering fibres (davictdi of Gagli- 

 ardi), resembling in character the ordinary white 



400. (Sharpey.) 



neighboring lamellae together, and may be drawn out when the latter are 

 torn asunder (Fig. 49). These perforating fibres originate from ingrow- 

 ing processes of the periosteum, and in the adult still retain their con- 

 nection with it. 



Development of Bone. From the point of view of their develop- 

 ment, all bones may be subdivided into two classes. 



