CONNECTIVE TISSUES BONE. 



71 



every part of the tissue. The size of the lacunae is to some extent pro- 

 portionate to that of the blood-corpuscles, being large in reptiles and 

 fish, and small in the higher classes of the vertebrata. In man their long 

 diameter is about T ^Vo tn of an inch, and their short g ' - th of an inch. 

 Every lacuna is occupied in the living bone by a corpuscle of " germinal 

 matter," which is the nutritive centre of the surrounding osseous sub- 

 stance. If, instead of a thin lamella of bone, sections of one of the long 

 bones be examined, it will be found that the penetration of the tissue by 

 bloodvessels renders a peculiar arrangement of the lacunre and canaliculi 

 requisite. The solid osseous texture which forms the shaft is covered by a 

 strong and firm layer of connective tissue termed the periosteum, in which 

 numerous bloodvessels ramify, and is lined by a very thin and delicate layer 

 of the same tissue, to which the term endosteum is applied. This also is 

 freely supplied with small vessels derived from the nutrient artery or arteries 

 of the bone. From both the external and internal membranes numerous 

 small bloodvessels penetrate the bone, occupying a series of canals that were 

 first described by Cloptou Havers, and have been named after him the Ha- 

 versiau canals. These for the most part rim parallel to the central cavity, 

 communicating however with one another by frequent transverse branches, 

 so that the whole system forms an irregular network, pervading every part 

 of the solid texture, and adapted for the establishment of vascular commu- 

 nication throughout. The diameter of the Haversian canals varies from 

 2Too tu to 2-oo tn f an incn or more; their average diameter may be stated 

 at about h of an inch. The Arteries and Veins usually occupy separate 



FIG. 32. 



FIG. 33. 





FIG. 30. Vertical section of Tibia, showing the network of Haversian canals. 



FIG. 31. Minute structure of Bone, as shown in a thin section cut transversely to the direction of the 

 Haversian canals: 1, One of the Haversian canals surrounded by its concentric lamella; the lacunae 

 are seen between the lamella;; but the radiating tubuli are omitted; 2, an Haversian canal with its 

 concentric laminae, lacunae, and radiating tubuli ; 3, the area of one of the canals; 4, 4, intervening 

 lamellce ; between these lamellie at the upper part of the figure, several very loug lacuuse with their 

 tubuli are seen. In the lower part of the figure, the outlines of two other canals are given, in order 

 to show their form and mode of arrangement in the entire bone. 



channels, and those inclosing the latter are, in some instances, as in the 

 diploe of the flat bones of the skull, of extraordinary amplitude. When a 

 transverse section of a long bone is made, the open orifices of the longitudinal 



