i8 PHYSIOLOGY FOR BEGINNERS CHAP. 



aorta, which carries the blood from the heart t<> the different 

 parts of the body. 



Leading up to the heart from below, deep in the thorax, is 

 a dark reddish purple coloured vessel, a vein, the inferior vena 

 cava, which brings the blood from the lower limbs and lower 

 part of the trunk, through the diaphragm, back to the heart. 

 Above the heart there is another large vein, made up by several 

 branches, which brings the blood back from the head and 

 upper limbs. This is the superior vena cava. 



In the thorax, on each side of the heart, is a soft, pinkish, 

 spongy organ ; this is the lung. The lungs are attached to 

 the vertebral column just under the heart, and by arteries and 

 veins to the base of the heart, but are otherwise free, and not 

 connected to the walls of the thorax. Each appears much 

 smaller than the half of the thorax in which it lies. The lungs 

 have collapsed, but when the animal was alive each lung was 

 filled and distended with air, and filled its side of the thorax. 

 Cut out a bit of one lung, notice how soft and light it is ; 

 it still contains some air, and if put in water will float. 



Make a cut downwards through the skin of the neck, 

 exactly in the middle line. Running down the middle of the 

 neck is a tube (partly covered by muscles, which should be cut 

 away), easily recognised, because there are a number of rings of 

 cartilage round it all along. This tube is the trachea. After 

 the trachea reaches the thorax, it divides into two branches, one 

 passing to each lung. Slit the trachea open with scissors, and 

 in this way trace it upwards. A little above the middle of the 

 neck it widens out into a box-like cavity, with walls of cartilage, 

 the larynx. The larynx opens above by a slit-like opening 

 into a wide space, the pharynx, which is continuous with the 

 mouth. Air from the mouth can pass through the larynx into 

 the trachea, and so to the lungs. Pass a penholder from the 

 pharynx downwards behind the larynx ; it will pass into a tube 

 lying underneath the trachea. This is the oesophagus, leading 

 to the stomach. 



Remove the skin from one of the hind limbs. Notice that 

 the fleshy part consists of muscles, running mostly lengthwise, 

 which can be more or less easily separated from one another. 

 Each muscle is fixed at its two ends, and some of them along 

 the deeper edge as well. They are fixed to bones. The 



