83 ANIMAL MKCHANIS.M. 



ferent branches, an example of which is seen in the internal 

 surface of the parietal bones of llio human skull. Even a vein 

 is able to i'mm a considerable hollow in a Lone. The ab- 

 nonual dilatation of those veins which are called varicose, and 

 which is usually produced in the legs, is accompanied with a 

 change of form in the anterior surface of the tibia ; the bone 

 wears tlic impress of the dilated veins. "We cannot say that 

 these osseous furrows enter into the pre-established plan of 

 nature ; that the skeleton had originally these furrows in 

 order to provide for the swollen state which should hereafter 

 be produced. Surgeons know that these hollows are formed 

 in the bone of an adult, which was in a perfectly normal state 

 before accident had caused the varicose dilatation of the veins. 



It is a similar mechanism which forms along the bones the 

 furrows imprinted by the muscles, and which gives to the 

 perineeum, for instance, the prismatic form by which it is 

 characterized. 



The hollows in which the tendons are lodged are not formed 

 hi 'fun 'hand in the skeleton; it is the presence of the tendon 

 which has hollowed them out, and which still maintains them. 

 Should a luxation take place and change the position of the 

 bone with respect to the tendon, the former furrow which is 

 now empty is gradually effaced ; at the same time a new- 

 furrow is fi ained, and by degrees assumes the necessary depth 

 to allow the tendon to repose in its fresh place. 



But, it may be said, that the articular surfaces, so perfect 

 in their structure, so well adapted to the movements which 

 they carry on, are certainly organs formed beforehand. Here 

 tin- bony surfaces are clothed with a polished cartilage 

 moistened with a synovial lluid which facilitates their move- 

 IIH 'lit still more ; all around them, fibrous ligaments prevent 

 the bones from passing the limits allotted to them, and the 

 Mirl'.iees from separating from each other. S<.> perfect an ap- 

 paratu- could not be formed by the. function alone. 



\Vr have hero at least a proof of the foresight of nature 

 and of tin- \\iMlnm of her plans. 



I.et ii- turn oner more to surgery, which will show us that 

 a Tier di>loi atioiis, the old articular cavities will be obliterated 

 and disappear, \\hile at the new point where the head of the 



