172 CIRCULATORY SYSTEM. 



case exceeded a minute. A film of coagulnm was generally per- 

 ceptible on the surface at the expiration of ten minutes. Each 

 parcel was firmly coagulated in twenty-five minutes. All the 

 coagula shewed buff about half an inch in depth ; seven of them 

 were very firm, of which five exhibited the surrounding edge 

 elevated and turned in, the other two being still more decidedly 

 cupped. In two out of the five not so firmly congealed, the 

 coagula were soft and flabby. The serum amounted in every 

 parcel to about o)te-haIJ' of the whole quantity. 



OF THE HEART AND PERICARDIUM. 



Situation. — The heart is inclosed within the pericardium ; and 

 both together occupy the middle space of the cavity of the 

 thorax. 



PERICARDIUM. 



The pericardium is a membrane formed into a conoid sac for 

 the purpose of containing the heart. It has, exteriorly, an opaque 

 white aspect; is dense in its consistence, and firm and tenacious 

 in its texture. It is composed of two layers, intimately united by 

 cellular tissue. The external one is dense and fibrous, is pos- 

 sessed of the chief strength of the membrane, and is attached be- 

 low by several ligamentary cords to the sternum and tendinous 

 part of the diaphragm, and above to the roots of the large blood- 

 vessels at the base of the heart, upon which we lose sight of it 

 altogether: the sides of it are clothed and additionally strength- 

 ened by the adhesions of the pleura;. The internal layer is fine 

 and cellular, exhibits inwardly a smooth, polished surface, and 

 appears to be similar to other serous membranes in its intimate 

 texture and organization. It not only lines the external layer, and 

 gives a covering to the roots of the large bloodvessels, but is re- 

 flected from them upon the heart itself, to which it forms a close 

 and complete tunic : so that the heart is absolutely out of (above) 

 the cavity of the pericardium ; in fact, it is situated precisely the 

 same in regard to this membrane as the human head is within a 

 double nightcap. 



The liquor pericardii is the pale yellow serous fluid found 

 within the cavity of the pericardium, secreted therein by the ex- 

 halents of the membrane. It serves to lubricate the contiguous 

 surfaces of the sac, and to preserve them against any ill conse- 

 quences from friction. 



J'he use of the pericardium is to confine the heart in its situ- 

 ation, to sustain it in its reciprocal action with the lungs, pre- 

 venting any undue collision, and to serve as a protecting fence to 

 the organ. 



