402 PHILOSOPHICAL TRANSACTIONS. [aNNO IGQI. 



an increase in the dimensions of the animal, and makes them more capable of 

 the accession of new particles to nourish and augment them. 



Coming to describe the nature and structure of the parts, which are the sub- 

 ject of the discourse, he begins with the periosteum, or membrane which invests 

 the bones, which consists of two sorts of fibres, one of which lying next to 

 the bone itself, is derived from the dura mater, the other from the tendons of 

 the muscles. The use of this membrane is to cover the bones ; to convey 

 spirits into them for their sense, and to assist in their nutrition, to which end 

 it has fibres inserted into them ; to limit their growth ; to keep some of them 

 conjoined ; to join the bones and their cartilages together ; to fasten the heads 

 and tendons of the muscles to the bones ; and lastly, for the safety and security 

 of the bones against injuries, as it serves to make them sensible, and so gives 

 the animal a quick apprehension of any mischief that threatens those parts, and 

 directs us in our application of remedies when they are injured. 



The bones, though they are at first gelatinous, and afterwards cartilaginous, 

 are when they come to their true and proper nature, solid and hard, consist- 

 ing of terrestrial and saline particles. These particles, being in their several 

 series united at their extremities, form strings, and these strings being united 

 make distinct plates, which lying one over another make the whole thickness 

 of the bone. In and between these plates he observes two sorts of pores, 

 some which run through every plate, others which are fornied between them 

 for the dispensation of the medullary oil to the substance of the bone. The 

 superficies of the bones is unequal, being rendered so by some superficial 

 cavities, and by passages which penetrate into them, the first of which are 

 for enlarging their surface, and strengthening the adhesion of their membrane 

 to them ; the other for the ingress of blood vessels into their substance or 

 cavities. The cavities of the bones are in some large, in others small and 

 numerous, whose partitions are formed of plates propagated wholly from those 

 plates which make the sides of the bones, in such as have long cavities ; and 

 in those which are spongy, from plates which run up the whole length of the 

 bone in that manner. And in some bones there are fasciculi of strings, which 

 run off from the plates in the sides, and make a sort of cancelli, or net-work in 

 the cavity. 



In the bones there are many blood-vessels, which serve for their nourish- 

 ment ; the arteries entering at one end, and the veins coming out in vast num- 

 bers, either at the contrary extremity, or in some intermediate parts : and there 

 are both veins and arteries belonging to the marrow. 



In the teeth he observes a twofold substance, one of a stony nature, which 

 is the cortical, or exterior part, of so much of the teeth as stands out of the 



