CLASSIFICATION OF THE BONES. 149 



The long bones consist of a shaft and two extremities, or 

 epiphyses, which are much looser in structure than the shaft, 

 are developed separately from it, and are supplied by numerous 

 blood-vessels passing directly into them. The shaft is com- 

 posed of very hard tissue, encloses a cavity called the medul- 

 lary canal, and on its outside a number of small lines or grooves 

 are to be seen, which are the oblique openings, through which 

 vessels pass from the periosteum into the dense structure of the 

 bone. 



The bones of race-horses contain more compact tissue in their 

 shafts than those of lower-bred animals. The dense struc- 

 ture — compact tissue — contains the Haversian canals, conveying 

 blood-vessels ; and the canaliculi, which are smaller canals con- 

 veying blood plasma to the lacunae. In this manner this portion 

 of the bone receives its supply of nutritious material from 

 the blood, and without this arrangement the bony structure could 

 not receive nutrition. Each Haversian canal is about -q^ of an 

 inch in diameter, and collectively they run in a longitudinal 

 direction, but have many transverse branches of communication. 

 The canaliculi average ts-.-d^ott of ^^ i^ch in diameter, and appear 

 as dark radiating lines, decreasing in diameter as they recede 

 from the lacunae ; they are, along with the lacunse, filled with 

 the fluid, colourless portion of the blood. 



The lacunse are irregularly oval, stellate, dark-looking bodies, 

 lying with their long diameters, which are about i -gVo ^^ ^^ inch, 

 parallel to the bony lamellae. Each long bone is, in addition 

 to the periosteal vessels, supplied by a nutrient artery, which 

 passes directly into the bone, and breaks up into branches in 

 the interior of the medullary canal. 



It will be seen that the compact bone is abundantly provided 

 with vessels, entering from numerous points, covered by perios- 

 teum and endosteum; that these nutrient vessels are exceed- 

 ingly minute, and surrounded by a dense structure ; and that, 

 in consequence of this peculiarity, the effects of inflammatory 

 action wiU be very distinctive, and the symptoms most acute. 

 Fortunately, however, inflammation of the shafts of the long 

 bones is exceedingly rare in the lower animals. The extremi- 

 ties or epiphyses of the shaft are, as already stated, developed 

 separately from the shaft, and they exceed it in circumference, 

 are irregular in outline, expanded, roughened externally, and 



