88 



ANIMAL MECHANISM. 



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

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

 is able to form a considerable hollow in a bone. The ab- 

 normal dilatation of those veins which are called varicose, and 

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

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

 wears the 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 

 beforehand 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 formed, and by degrees assumes the necessary depth 

 to allow the tendon to repose in its fresh place. 



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

 in their structure, so well adapted to the movements which 

 they carry on, are certainly organs formed beforehand. Here 

 the bony surfaces are clothed with a polished cartilage 

 moistened with a synovial fluid which facilitates their move- 

 ment still more ; all around them, fibrous ligaments prevent 

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

 surfaces from separating from each other. So perfect an ap- 

 paratus could not be formed by the function alone. 



We have here at least a proof of the foresight of nature 

 and of the wisdom of her plans. 



Let us turn once more to surgery, which will show us that 

 after dislocations, the old articular cavities will be obliterated 

 and disappear, while at the new point where the head of the 



