/'///: IIKM.'T. 



511 



The ItfHijihutli-x follow the arteries, passing alung tho visceral layer of 

 the pericardium, uiul entering the dust, r of jrlands situated near the base of 

 tin: heart. (The endocardium, especially in the ventricles, has a network 

 of lino lymphatics, the walls of which consist of only a single layer of 

 intimately-adhering cells. None have been traced upon the chordae teudiuefc, 

 ,ind very few upon the uuriculo-ventricular and semilunar valves.) 



The ni rri's of the heart, furnished by the cardiac plexus, come from tho 

 pnempOgMtrie and sympathetic. The tubes are small, and show some cells 

 in their course. In addition to these, the heart is provided with a particular 

 uanglionic system, to which Rcmak has called attention. It is believed that 

 there exist three ganglia in different points of tho cardiac parietes, and that 

 on these depend the movements of the orgun. (According to Carpenter, the 

 nerves of the heart are : 1, Minute ganglia and fibres of tho sympathetic, 

 situated in the walls of the cavities, and especially in the auriculo- 

 ventricular furrow ; 2, Fibres derived from the cervical portion of the 

 sympathetic, and passing to tho cardiac plexus, between tho aorta and 

 pulmonary artery ; 3, Cerebro-spinal fibres entering the inferior cervical or 

 stellate ganglion, and proceeding to the same plexus, and probably derived 

 from a centre situated in the brain and spinal cord ; and, 4, Fibres coursing 

 in the vagus, and originating in a centre situated in the medulla oblongata. 

 The first three of these ganglia and fibres probably collectively con- 

 stitute the excito-motor system of the heart, the fourth is an inhibitory, 

 restraining, or regulo-motor centre.) 



D. SEROUS MEMBRANES OF THE HEART. These are three in number : 

 two internal, or endocardial, one of which occupies the right, the other the 

 left cavity ; and an external, a dependency of the fibro-serous sac which 

 contains the heart. 



1. Internal serous membranes, or endocardia. These two membranes, 

 independent, like tho cavities they line, are spread over the auricular and 

 ventricular walls, covering the tendinous or muscular columns attached to 

 these walls, and are prolonged into the veins and arte- 

 ries, to form tho internal tunic of these vessels. At 

 the auriculo-ventricular and arterial openings, they con- 

 stitute a duplicaturo for the valves situated there. 

 These valves are, therefore, due to tho projection of a 

 circular fold of the endocardia, between the two layers 

 of which a thin prolongation of tho fibrous zones from 

 tho base of the heart is insinuated. In tho auriculo- 

 ventriculur valves there is also found, beneath the 

 internal or superior layer, muscular fibres furnished by 

 the auricles. 



The endocardium of the right heart has a red tint, 



which is deepest in tho ventricle. In the left heart, 



this tint is slightly yellow, especially in tho walls of 



the auricular appendix, which may be attributed to the 



n- -e of a thin layer of yellow clastic tissue that 



ra the adherent face of the membrane. 



(Tho endocardium consists of three layers: 1, A 



thin bed of white fibrous tissue, connecting it to tho 



muscular structure; 2, A middlo layer, composed of 



which is very abundant in the auricles; 



and :!, An epithelium, consisting of a single or double 



: of somewhat elongated, polygonal, pavement nucleated cell-.; 



Fig. 204. 



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L, NIK I.-.ito 1 ii-lls MX. 

 .suiiiiir,' tin' fusiform 



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