174 



Topography. 



51C. Topography of the Thoracic Viscera. 



The heart is contained in a conical, membranous sac, the Peri- 

 cardium, the apex of which is directed upwards and surrounds the great ves- 

 sels, the base of which is attached to the central tendon of the diaphragm. 

 The pericardium consists of an external and an internal layer; the former 

 has the structure of fibrous, the latter of serous membranes. The serous 

 layer invests the heart, and is then reflected on the inner surface of 

 the pericardium; it consists, therefore, of a visceral and a parietal 

 portion. The fibrous layer is continued above for some distance along 

 the large blood-vessels in the form of tubular prolongations, which 

 become gradually lost upon their external coats. 



