512 Tin: CIRCPLATOBY APPARATUS, 



2. /-'./////'// gcrnux NMM&fOM. Tliis is tho visceral lining membrane of 

 the pericardium, tho description of which follows. 



5. TJie Pericardium. (Fig. 234, o.) 



Preparation. Place tho animal in tho second position, and remove the sternal rilis l.y 

 separating the cartilages and luxating their costo-vertebral articulations. 'I'his pro- 

 cedure (MTinitd tho study of tho situation and gnu-nil disposition of tho h, art and 

 \> riivinlinm. But in order more easily to examine tlie reciprocal arrangement <>! 

 two parts, it is necessary to extract them from the thoracic cavity by tearing through tin- 

 sternal insertion of the pericardium. 



The pericardium, or proper serous membrane of tho heart, is a membranous 

 sac inclosing that organ, fixing it in tho thoracic cavity, and favouring its 

 movements by its polished surface. 



This sac is formed by a fibrous layer, within which is spread a serous 

 membrane, divided into two parts one parietal, the other visceral. 



The fibrous layer of the pericardium presents somewhat tho general form 

 of the heart Its internal surface is covered by tho parietal portion of the 

 serous membrane. The external surface corresponds to the two laminae of 

 tho mediastinum. Its summit (or apex), depressed on each side, and elon- 

 gated from before to behind, is firmly attached to the superior face of tho 

 sternum, from tho fourth rib to the origin of the xiphoid cartilage. By 

 its base, it is fixed to the large vessels going to and leaving the heart, where 

 it is continuous with their cellular sheath, and where it sends some fibres to 

 the longus colli. 



Tho serous membrane of the pericardium has been well compared by 

 Bichat to a cotton night-cap, tho external part of which would represent tho 

 parietal layer, and tho inverted part the visceral division of that membrane. 

 The parietal layer adheres in tho most intimate manner to tho internal face 

 of tho fibrous tunic, and is seen to be reflected, to form tho visceral portion, 

 around the pulmonary arteries and the aorta to a certain distance from 

 their origin, and on tho pulmonary veins. Tho visceral layer envelops 

 in common the two arterial trunks, covers a small part of the veiiro cavro, 

 particularly tho anterior, spreads over the insertion of tho pulmonary veins, 

 and then descends on tho auricles and ventricles. Tho free face of this 

 layer is in contact with that of the parietal layer; tho adherent face is 

 applied to tho tissue of tho heart or that of tho large vascular trunks, except 

 at tho horizontal and vertical grooves, where it rests on tho coronary vessels, 

 and on the mass of adipose tissue constantly accumulated on their track. 



In tho living animal, the cavity of tho pericardium is never entirely 

 filled by tho heart, whoso movements are, therefore, allowed much more 

 liberty. Otherwise, as it does not contain any gas, nor a sensible proportion 

 of fluid, 1 its walls are immediately applied to the surface of tho heart. 



Blood reaches the pericardium by tho mcdiastinal arteries. Its walls 

 receive some sympathetic nerve-fibres. 



(The pericardium is composed of a fine network of elastic fibres adhering 

 to tho muscular structure of tho heart by ono surface, and covered by a 

 single or double layer of tcsselated epithelium on the other. Gurlt, in 1867, 



1 With horses in health, the fluid exhaled into the pericardium is barely sufficient to 

 moisten and lubrify the free surface of its m T> .IM inrnil>raiie. But in those worn out ;m<l 

 enfeebled by age, privations, or disease, it is not rare to M c it iuviimiilut< il in greater or 

 IC*B quantity. To verify this, however, an examination ought to take pla-'e //,//. ,1,'nl, lij 

 after death, as the accumulation of fluid in the serous cavities by cadaveric exhalation is 

 common in all animal?. 



