30 THE FROG CHAP. 



The trunk is hollowed out into two cavities : the ab- 

 dominal or body-cavity (ccelome) below, and the neural 

 canal above ; of these the neural cavity alone is continued 

 into the head. The abdominal cavity contains the 

 greater part of the enteric canal, the liver, gall-bladder, 

 pancreas, spleen, lungs, heart, kidneys, urinary bladder, 

 and reproductive organs. The neural canal contains the 

 brain and spinal cord. The anterior end of the enteric 

 canal is continued forwards into the head, forming the 

 mouth-cavity, and opens externally by the aperture of 

 the mouth ; its posterior end opens externally by the 

 vent. The enteric canal passes through the containing 

 body-cavity, having no communication with it. The 

 lungs open into the pharynx, and thus communicate 

 with the exterior not only by the mouth but also by the 

 nostrils. The kidneys, bladder, and oviducts communi- 

 cate with the cloaca, and thus with the exterior through 

 the vent. Neither the neural nor the abdominal cavity 

 has any communication with the exterior. The walls 

 of the head and trunk consist largely of muscles and 

 bones covered with skin. The limbs are solid outgrowths 

 of the trunk, formed mainly of muscle, with bony 

 supports and a covering of skin. 



Organs. Notice that the body consists of various 

 definite structures, or organs as they are technically 

 termed, which have various purposes or functions to 

 perform. The enteric canal, together with the liver and 

 pancreas, are organs of digestion ; the lungs and skin, 

 organs of respiration or breathing ; the heart and blood- 

 vessels organs of circulation, serving as they do to propel 

 and conduct the blood through the body ; the kidneys, 

 aided by the skin, organs of excretion, for getting rid of 

 waste matters ; the ovaries and spermaries, organs of 

 reproduction ; the muscles, organs of movement ; the 

 brain and spinal cord, together with the nerves, organs 



