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CHAPTER X. 

 OF THE VISCERA. 



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

 named splanchnology, from the Greek words <r?rXay^;vav, viscus, and 

 Xayaj. The viscera of the human body are situated in the three 

 great internal cavities : cranio- spinal, thorax, and abdomen. The 

 viscera of the cranio-spinal cavity, namely, the brain and spinal cord, 

 with the principal organs of sense, have been already described, 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, kidneys, 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 by the sternum, six superior costal cartilages, ribs, and inter- 

 costal muscles in front ; laterally., by the ribs and intercostal muscles ; 

 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 inferi- 

 orly, by the diaphragm. This cavity is much deeper on the posterior 

 than on the anterior wall, in consequence of the obliquity of the dia- 

 phragm, and contains the heart enclosed in its pericardium, with the 

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

 oasophagus ; some important nerves ; and, in the foetus, 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. 



Pericardium. The pericardium is a fibro-serous membrane like the 

 dura mater, and resembles that membrane in deriving its serous layer 

 from the reflected serous membrane of the viscus which it encloses. 



