THE RABBIT 



421 



secrete an oily substance into the hair follicles. The glands 

 and follicles are parts of the epidermis, but project inwards 

 into the dermis. Below the latter is a layer of fatty tissue. 

 The muscles of the adult rabbit, as in the frog, show little 

 trace of the segmentation which they have in the early 

 stages of development. The general arrangement of the 

 internal organs resembles that of the frog, but a muscular 

 partition, the midriff or diaphragm, separates off from the 



Fig. 308. — A diagram of a transverse section through the thorax of » 



rabbit. 



a. wed., Ventral part of mediastinum; at>., aorta; i.v.c, inferior vena cava; /.z»., 

 left ventricle ; ces., oesophagus ; /.<:., pericardial cavity ; p.med., dorsal part of 

 mediastinum ;j*w., pericardium ; r.I., right \\m%\r.pl., right pleura; r.pl.c, 

 right pleural cavity ; r.v, , right ventricle; s/>.c, spinal cord; st. t sternum; »., 

 vertebra. 



peritoneal cavity of the abdomen a chest or thorax in the 

 breast region, where lies the pericardium, with on each side 

 a pleural cavity, into which the lung of its side projects. 

 The lining of each pleural cavity is known as a pleura, and 

 of course covers the lung as well as the inside of the thorax. 

 The heart in its pericardium does not lie free in the cavity 

 of the chest, as that of the frog does in the anterior part of 

 its pleuroperitoneal cavity, but is fastened to the dorsal and 

 ventral walls of the thorax by a double sheet of membrane, 



