I7 6 



PRACTICAL HISTOLOGY. 



[xnt. 





outermost row of lacunae will be found to form loops and open into 

 the lacunae from which they arose : these are recurrent canaliculi 

 (fig, 147, a). The canalicular system is for the distribution of 

 lymph to all the parts of the calcined fibrous matrix. Notice also 

 that the intermediary lamellae are parts of circles with a much 



larger radius than those 

 of the Haversian system. 

 Each Haversian canal, 

 with its system of lamel- 

 lae, lacunae, and canali- 

 culi, forms a Haversian 

 System. The greatest 

 diameter of the lacuna) is 

 about 14 p. ( T Vo iw'h)- 



(d.) The lamellae in a 

 Haversian system on 

 transverse section appear 

 as thin concentric bands, 

 a clear transparent one 

 alternating with one which 

 looks more granular. 

 These are not due to 

 different kinds of lamellae, 

 but in the clear ones one 



FIG. 146. T.S. The Shaft of a Human Femur. 

 Haversian canals; s. Haversiau lamellae; si. In 



looks upon the long axis 



of the fibrils composing the lamella, and in the others upon the 

 ends of the fibrils. 



2. L.S. of Dense Bone, prepared in the same way. 



(a.) (L) Observe Haversian canals running chiefly in the long 

 axis of the section, with here and there oblique, short, junction 

 canals. Near the surfaces some open externally, and others com- 

 municate with the medullary cavity. The lamellae of any Haver- 

 sian system run parallel to its own Haversian canal. In the 

 system of canals each 20-100 ^ wide the canals frequently 

 divide dichotomously, and ultimately form a network in the com- 

 pact bony substance. 



(b.) If the section be near the surface of the bone, so as to 

 include the peripheric lamellae, canals for blood-vessels, perforating 

 the lamellae and not surrounded by lamellae as in the Haversian 

 systems, may be seen. They are called Volkmann's canals, and 

 contain the perforating vessels. They are connected with the 

 Ilaversian canals proper. They are well seen in sections of the 

 femur of a guinea-pig, but, unlike Haversian canals, they are not 

 surrounded by Ilaversian or concentric lamellae. 



(c.) (H) Observe the flattened oval lacunae with their canaliculi; 



