202 NATURAL THEOLOGY. 



how firmly every part must be secured, how care- 

 fully surrounded, how well tied down and packed 

 together. 



This property of animal bodies has never, I 

 think, been considered under a distinct head, or so 

 fully as it deserves. I may be allowed therefore, 

 in order to verify my observation concerning it, to 

 set forth a short anatomical detail, though it oblige 

 me to use more technical language than I should' 

 wish to introduce into a work of this kind. 



1 . The heart (such care is taken of the centre 

 of life) is placed between two soft lobes of the 

 lungs ; is tied to the mediastinum and to the peri- 

 cardium ; which pericardium is not only itself an 

 exceedingly strong membrane, but adheres firmly 

 to the duplicature of the mediastinum, and, by its 

 point, to the middle tendon of the diaphragm. 

 The heart is also sustained in its place by the 

 great blood-vessels which issue from it.* 



2. The lungs are tied to the sternum by the 

 mediastinum before; to the vertebrae by the pleu- 

 ra behind. It seems indeed to be the very use of 

 the mediastinum (which is a membrane that goes 

 straight through the middle of the thorax, from 

 the breast to the back) to keep the contents of 

 the thorax in their places ; in particular to hinder 

 one lobe of the lungs from incommoding another, 

 or the parts of the lungs from pressing upon each 

 other when we lie on one side.f 



*Keill's Anat. p. 107, ed. 3. f lb. p. 119, ed. 3. 



