Near the hindmost pair of _ribs_ note a sheet of muscles, the _diaphragm_, which extends across the body-cavity, dividing it into an anterior portion, the _thoracic cavity_, and a posterior, the _abdominal cavity_. What are the most conspicuous organs in the thoracic cavity? Leading anteriorly to the mouth-cavity is a long tube, the _trachea_, composed of a series of cartilaginous parts of rings placed end to end. Note at its anterior end the _glottis_ and _epiglottis_. Insert a blowpipe into the glottis and inflate the _lungs_, which will fill all the otherwise unfilled space in the thoracic cavity. The abdominal cavity contains the _viscera_ suspended in a fold of the lining membrane, as in the other vertebrates studied. Note lying against the diaphragm a large, red, glandular structure, the _liver_. Separate the two large lobes of the liver and expose the opalescent _gall-bladder_. By passing a canula into this and ligaturing, the _cystic duct_ may be injected. Beneath the liver is a large loop-shaped expansion of the alimentary canal, the _stomach_. Arising from the right end of the stomach is the narrow _duodenum_, which gradually merges into the very much convoluted _small intestine_, or _ileum_, which is followed by the _large intestine_, or _colon_, the last part of which is a straight tube, the _rectum_. The small intestine occupies most of the space in the peritoneal cavity. Within the loop of the pylorus will be found an irregular pinkish mass of tissue, the _pancreas_. Beneath the stomach on the left side of the body lies a very dark glandular mass not much unlike the liver but altogether detached from it. This structure is the _spleen_, a ductless gland.