174 



STRUCTURE AND ENDOWMENTS OF ANIMAL TISSUES. 



traced to a considerable distance. These spots, known as the osseous 

 corpuscles (sometimes termed the Purkinjean corpuscles, after the name 

 of their discoverer), are highly characteristic of the true bony structure, 

 being never deficient in the minutest parts of the bones of the higher 

 animals, although those of Fishes are frequently destitute of them. 

 These corpuscles were formerly supposed, from their dark appearance, 

 to be opaque, and to consist of aggregations of calcareous matter which 

 would not transmit the light : but it is now quite certain, that they are 

 lacunce or open spaces ; and that the radiating prolongations from them, 

 which are far smaller than the minutest capillary vessel, are canaliculi^ 

 or delicate tubes. Of these canaliculi, some may be seen to interlace 

 freely with each other, whilst others proceed towards the surface of the 

 bony lamella ; and thus a system of passages, not by any means wide 

 enough to admit the blood-corpuscles, but capable of transmitting the 

 fluid elements of the blood, or matters selected from them, is established 

 through the whole substance of the lamella. 



291. The lacunae of Human bone have an average length of l-1800th 

 of an inch ; and they are usually about half as wide, and one-third as 

 thick. The diameter of the canaliculi is from l-12,000th to l-20,000th 

 of an inch. Their size and form differ greatly, however, in the different 

 classes of Vertebrata ; so that it is usually possible to refer a mere frag- 

 ment of bone to its proper group, by an examination of its minute 

 structure. The succeeding figure represents the arrangement of these 

 lacunae and canaliculi in the bony scale of a fish (the Lepidosteus) ; 

 which is almost the only existing representative of a large class of bony- 

 scaled Fishes, that formerly tenanted the seas. Its lacunae will be 

 seen to differ greatly in form from those of human bone ; and the 

 canaliculi which proceed from them are much fewer in number. The 

 purpose of this penetration of the osseous texture by such a complicated 

 apparatus of tubuli, can scarcely be anything else than the maintenance 



Fig. 47. 



Section of the bony scale of Lepidosteus ; a, showing the regular distribution of the lacunaB and of 

 the connecting canaliculi; b, small portion more highly magnified. 



of its vitality by the continual percolation of nutrient fluid, drawn into 

 the system of lacunae and canaliculi from the neighbouring blood-vessels. 

 Thus the nutrition of the ultimate osseous texture, though carried on 

 upon the same general plan with that of Cartilage, differs in this : 

 that there is a provision in Bone for the ready transmission of nutrient 

 matter through its texture, by means of minute channels, which does 

 not exist in Cartilage ; a difference obviously required by the greater 

 solidity of the substance of the former, which does not allow of the 

 diffused imbibition, that is permitted by the softer and moister nature 

 of the latter. We shall presently find that these channels are only 





