296 



OF THE CIRCULATION OF THE BLOOD. 



FIG. 119. 



Anastomosing muscular fibres of the 

 Heart seen in longitudinal section. 

 On the right the limits of the separate 

 cells with their nuclei are exhibited 

 somewhat diagrammatically. 



view the muscular tissue of the heart is characterized by containing a larger 



amount of water than other muscles (79, in- 

 stead of 76 per cent.) ; a considerable quantity 

 of a peculiar kind of sugar, iuosite, a very 

 small proportion of creatin, and a large amount 

 of creatinin. 1 The nerves of the heart are de- 

 rived from the cardiac plexus, which is formed 

 by branches from the pneumogastric and sym- 

 pathetic nerves, and appear in the form of 1. 

 Minute ganglia and gaugliouic cells, situated 

 in the walls of the cavities, and especially in 

 the auriculo-ventricular and interventricular 

 furrows. Some of the ganglionic cells resem- 

 ble those of the sympathetic in giving off from 

 one and the same pole a straight and a spiral 

 fibre ; others are bipolar ; and others again 

 form bicelled ganglia, resembling two pears 

 applied to each other by their broad ends, the 

 stalks representing the nerves they give off. 

 These have no spiral fibre. 2. Fibres derived 

 from the cervical portion of the sympathetic, 

 which pass to the cardiac plexus, between the 

 aorta and pulmonary artery. 3. Cerebro- 

 spinal fibres which enter the inferior cervical 

 or stellate ganglion and proceed to the same 

 plexus, and are 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 constitute the excito- 

 motor system of the heart, the fourth forms an inhibitory, restraining, or 

 regulo-motor apparatus. The precise mode of termination of the nerve-fibres 

 has not been made out, but they probably lose their double contours, and 

 continuing their course as pale fibres form loops and anastomoses around the 

 muscle cells. 2 It will be observed that in consequence of the absence of a 

 sarcolemma the ultimate nervous plexus is in immediate contact with the 

 contractile substance. The nerves of the parietal layer of the Pericardium 

 are derived according to Luschka from the right vagus (ramus recurrens), 

 and phrenic, 3 and Schweigger-Seidel has observed a rich plexus of nerves in 

 the endocardium. According to Eberth and Belajeff,* the endocardium, es- 

 pecially in the ventricles, and both surfaces of the pericardium, present a 

 meshwork of fine lymphatics, the walls of which in some parts consist only 

 of a single layer of intimately-adhering cells. No lymphatics are traceable 

 on the chorda? tendinerc, and very few upon the auriculo-ventricular and 

 semilunar valves. We shall now examine what agency in the Human Cir- 

 culation may be attributed to the Heart, the Arteries, and the Veins re- 

 spectively ; and what other forces may be fairly presumed to operate in the 

 Capillary circulation. 5 



1 Kunke, (Jnmd/uge d. PhyMolog., 1868, p. 307. 



'- Lan^erlians, Virchow's Archiv, Band Iviii, 1873, p. 71. 



5 Frey, Marker's Translation, 1874, p. 403. 



4 Yirehow's Archiv, 18(J(3, Bd. xxxvii, p. 55. 



5 Many of the phenomena of the circulation can be conveniently studied, and prac- 

 tice in the use of recording instruments, manometer, sphygmograpb, kymographion, 

 etc., obtained by means of an india-rubber model of the circulatory system cons true ted 

 by Dr. Rutherford, and described in the Journal of Anatomy and Physiology, vol. 

 v'i, p. 249. 



