



CHAPTER X. 



OF THE VISCERA. 



THAT part of the science of anatomy which treats of the viscera 

 is named splanchnology, from the Greek words tfirXay^vov, viscus, 

 and Xo'yo?. The viscera of the human body are situated in the three 

 great internal cavities, the cranio-vertebral, thorax, and abdomen. 

 The viscera of the cranio-vertebral cavity the brain and spinal 

 cord, with the principal organs of sense have been already de- 

 scribed, in conjunction with the nervous system. The viscera of the 

 chest are the central organ of circulation, the heart ; the organs 

 of respiration, the lungs ; and the thymus gland. The abdominal 

 viscera admit of a subdivision into those which properly belong to 

 that cavity, viz. the alimentary canal, liver, pancreas, spleen, kid- 

 neys, and supra-renal capsules, and those of the pelvis the bladder 

 and internal organs of generation. 



THORAX. 



The thorax is the conical cavity, situated at the upper part of the 

 trunk of the body; it is narrow above and broad below, and is 

 bounded in front by the sternum, six superior costal cartilages, ribs, 

 and intercostal muscles ; laterally, by the ribs, and intercostal mus- 

 cles ; and, behind, by the same structures, and by the vertebral 

 column, as low down as the upper border of the last rib and the 

 first lumbar vertebra ; superiorly, by the thoracic fascia and first 

 ribs ; and, inferiorly, by me diaphragm. It is much deeper on the 

 posterior than on the anterior wall, in consequence of the obliquity 

 of the diaphragm, and contains the heart, enclosed in its pericardium, 

 with the great vessels ; the lungs, with their serous coverings, the 

 pleurae ; the ossophagus; some important nerves ; and, in the fetus, 

 the thymus gland. 



THE HEART. 



The central organ of circulation, the heart, is situated between 

 the two layers of pleura, which constitute the mediastinum, and is 

 enclosed in a proper membrane, the pericardium. 



