PERICARDIUM. 185 



lar covering of the arteries, in accompanying them to a great 

 distance.* 



The pericardium is a double membrane, or consists of two 

 layers, an internal and an external one. The external mefn- 

 brane, to which the preceding description is especially applica- 

 ble, resembles strongly the dura mater, but is thinner; it is, 

 therefore, white, semi-transparent, fibrous, and inelastic. Its 

 thickness is greater on the sides than below, where it rests upon 

 the diaphragm, or above, where it goes along the great vessels : 

 its fibres are irregularly disposed and interwoven, but many 

 may be traced longitudinally. 



The internal membrane lines the external, and gives the po- 

 lish to its cardiac surface; it is then conducted alon-g the sur- 

 face of the several vessels that have been mentioned, to the 

 heart, over the whole of which it is spread, and adheres to it 

 by cellular substance, frequently containing much adipose mat- 

 ter: it also causes the heart to have a smooth shining surface. 

 This is a very delicate thin serous layer; and secretes >a fluid, 

 transparent and somewhat unctuous, like that of the joints, but 

 riot so consistent; which lubricates the surface of the heart and 

 permits it to play freely within its pericardium. This fluid, in 

 a natural state, seldom exceeds a tea-spoonful, though two 

 ounces, or a little more, are not considered sufficient evidence 

 of a pathological state: its augmentation constitutes a dropsy. 



After death, we find the pericardium lying loosely around the 

 heart, from the vacuity, and consequently diminished bulk of 

 the latter; but while the circulation is going on, the heart fills 

 and distends it. A striking resemblance is observable between 

 the condition of the pericardium and the moveable articulations. 

 Its external layer corresponds with the strong fibrous capsule 

 that passes from one bone to the other; while the internal is the 

 synovial bag, which scarcely assists in the strength of the ap- 

 paratus, but secretes a fluid to render motion easy. 



Several instances are on record of a total absence of peri- 

 cardium. 



The Right Auricle (Auricula Dextra, anterior) is an oblong 

 cuboidal cavity. It is joined at its posterior superior angle by 



* Sabatier, Trait. d'Anat. vol. ii. p. 284. 

 17* 



