THE RABBIT. 249 



It should be noted that the venous and arterial systems 

 roughly correspond to each other in the distribution of 

 their parts. 



The Respiratory System. That the lungs are envel- 

 oped in the pleura, that they are attached at their ante- 

 rior end, and float freely behind, within the thoracic 

 cavity, have already been noted. That they communicate 

 anteriorly with a pair of bronchi, which unite into the 

 trachea, will have been noticed in the dissection of the 

 blood vessels. How many lobes are there in the right 

 lung ? In the left ? 



Observe that bronchi and trachea are made up of a 

 series of cartilaginous rings. On which side of the trachea 

 are these rings thickest, and why ? Note the absence of 

 any distinguishable syrinx at the division of the trachea 

 into bronchi. The voice organ in the rabbit is the 

 larynx, developed at the anterior end of the trachea. 

 The epiglottis stands at its anterior ventral border. It 

 is slightly wider and firmer than other parts of the 

 trachea. Dissect the larynx free from all its lateral 

 attachments, and observe that it is composed chiefly of 

 two rings of cartilage. The anterior one is wide in front, 

 but incomplete dorsally. It is called the thyroid cartilage. 

 The posterior one is a complete ring, wider on its dorsal 

 side. It is called the cricoid cartilage. 



Make a median ventral slit down the larynx, and draw 

 apart the severed edges. Observe the thin sheets of 

 muscle and connective tissue which bind the cartilages 

 together. Two little nodules of cartilage within the 

 larynx, and on the dorsal side, are the arytenoids. 



The two shallow, lateral depressions on the inner side 

 of the walls of the larynx are the ventricles. The pair of 

 delicate folds which form the posterior boundaries of the 

 ventricles are the vocal cords. These are folds of the 



