164 Human Physiology. 



With most of the internal organs it is different. The symme- 

 trical body is seen, in Fig. 17, to be filled with organs as- 

 unsymmetrical as an oyster. The heart lies across the centre 

 of the body, and though it has its right and left auricle and 

 ventricle, neither it nor the great arteries and veins within 

 the body can be considered as having symmetry. The lungs 

 have two lobes on one side, and one on the other. The 

 liver fills a large irregular space on the right side, the spleen on 

 the left, while the stomach, small or large, according as it is 

 full or empty, lies across the centre, and the abdomen is filled 

 with the convolutions of the small and large intestines. The 

 kidneys, bladder, and the organs of generation are, however, 

 symmetrical. 



In the human body we have, first, a bony frame-work or 

 skeleton, which gives it its general form, proportions, and 

 strength. A spinal column of twenty-four cylindrical bones, 

 with processes which make a bony canal for the spinal chord, 

 or tail-like extension of the brain. This column is a marvel of 

 strength and flexibility. Between the bones are elastic cushions 

 of cartilage, which protect the brain from jar. These cushions 

 are constantly lubricated by a glairy fluid secreted from the 

 blood for that purpose. The bones are bound together by 

 strong tendons, so as to allow a certain amount of motion 

 how much, those can tell who have seen the performances 

 of gymnasts and l! india-rubber men." And the movements 

 of every bone in the spine are made by numerous muscles, 

 placed with the nicest art to make one bone move upon the 

 other. 



At the top of the spine one of its bones and its processes 

 have expanded into thin double plates so as to form the skull 

 and protect the brain. Eight bones are formed into an egg- 

 shaped box, and, with hard and soft membranes, and the scalp 

 and hair, protect the seat of sentient life. The brain as it lies 

 in the skull is well shown in Fig. 18. The upper part of the 



