OF THE APPENDAGES TO BONE. 91 



inter-articular cartilages in the horse's body ; two between 

 the articulations of the lower jaw ; and two within each of 

 the stifle joints. They are peculiar only for their situation ; 

 and in no way differ from other substances of the same 

 description. The powers of life in cartilages, though small, 

 yet are fully evinced by their liability to take on inflam- 

 mation ; and to ossify, which disposition appears more com- 

 mon and universal in those of the horse species than of any 

 other known animal ; there being very few cartilaginous 

 parts in him that have not been found partially converted 

 into bone ; either by age, or the stimulus of great exertion, 

 &c. ; from which we readily perceive why stiffness and 

 want of elasticity are the consequences of these states ; from 

 the elasticity of the cartilages decreasing. The ulceration 

 of cartilage, from its slight vascularity, is necessarily very 

 slow ; as we witness in its attack on the navicular bone ; 

 and in the lower bones of the hock ; but from the stimu- 

 lating effects of the atmosphere this ulceration proceeds 

 much quicker at the ends of bones, where an opening into 

 the joint has been made. It is not ascertained that true 

 cartilage is ever reproduced ; but a cartilago-Hgamentous 

 substance is substituted sometimes by healthy granulations. 



The periosteum is a general investing fibrous membrane to 

 bones ; receiving different names as it covers different parts ; 

 that investing the skull being called pericranium, &c. The 

 uses of the periosteum appear to be to act as the medium 

 whereby vessels are assisted in the ingress and egress to 

 part of the bone ; and also to afford attachment to tendons. 

 Periosteum, in a healthy state, has no sensation ; but, like 

 some other parts, wlien diseased it becomes very sensitive. 



The medulla or marrow is a soft fatty matter, deposited in 

 the interior of bones ; particularly of the long ones, by means 

 of little membranous sacs, which do not communicate, or 

 the marrow would gravitate ; and which, as keeping the 

 unctuous matter distinct fi'om the bones, convinces us that 

 the use of this oil is not that of preventing brittleness in 

 them. The medullary vessels secrete the marrow within 

 these cells ; which secretion, being in itself wholly in- 

 organic, confutes the foolish notion of the exquisite sensi- 

 bility of the marrow. 



