Xlil 



PHYLUM CHORDATA 



453 



Respiratory Organs. The larynx (Fig. 1103) is a chamber 

 with walls supported by cartilage, lying below and somewhat 

 behind the pharynx, with which it communicates through a slit- 

 like aperture. The cartilages 

 of the larynx are, in addition 

 to the epiglottis, which has 

 been | already referred to 

 (p. 448), the large thyroid 

 (tli.}, which forms the ventral 

 and lateral walls, the ring-like 

 cricoid (cr.), the two small 

 arytenoids (ary.}, and a pair 

 of small nodules, the carti- 

 lages of Santorini (sant.), situ- 

 ated at the apices of the 

 arytenoids. The vocal cords extend across the cavity from the 

 thyroid below to the arytenoids above. Leading backwards from 

 the larynx is the trachea or wind-pipe (Fig. 1099, tr.), a long tube 



the wall of which is sup- 

 ported by cartilaginous 

 rings which are incomplete 

 dorsally. The trachea en- 

 ters the cavity of the 

 thorax, and there divides 

 into the two bronchi, one 

 passing to the root of each 

 lung. 



The lungs (Fig. 1104) are 



FlG. 1103. Lepus cuniculus. Laryux. A, 

 ventral view ; B, dorsal view. ary. arytenoid ; 

 cr. cricoid ; ep. epiglottis : sant. cartilage of 

 Sautorini ; th. thyroid ; tr. trachea. (From 

 Krause, after Schneider.) 



cent 



aort 



oes 



-pt.cav 



I. Z/*,^* , enclosed in the lateral parts 



of the cavity of the thorax. 

 Each lung lies in a cavity, 

 the pleural sac, lined by a 

 pleural membrane. The 

 right and left pleural sacs 

 are separated by a con- 

 siderable interval owing to 



FIG. 1104. Lepus cumculus. Diagram of a , .... . = 



transverse section of the thorax in the region of the tne development in tne 



ventricles to show the relations of the pleurae, meiiia- . QT ,f,>; nrl V> f,, 700rl thorn n f 



stiiium, etc. The lungs are contracted, aort. dorsal P ar ,VW& 



aorta; az.v. azygos vein; cent, centrum of thoracic a a-nopp thp mprlinstinnm 



vertebra; l.lng "left lung; l.pl. left pleural sac; ? Space, I im, 



l.vent. left ventricle ; my. spinal cord ; oes. ceso- m which, aS already 6X- 

 phagus ; par. per. parietal layer of pericardium ; pt. i j r ,1 i j 



can. post-caval, close to its entrance into right auricle ; plained, lie tne neart and 



r.lny. right lung ;r.pl, right pleural cavity ; r.vent. right n fhpr nro-{in<? Thp Inner i 

 ventricle ; *(. sternum ; v.med. ventral mediastinum. ' J -g al u^e, - 1 



attached only at its root, 



where the pleural membrane is reflected over it. In this respect 

 it differs widely from the lung of the bird. It differs also in its 

 minute structure. The bronchus, entering at the root, divides 

 and subdivides to form a ramifying system of tubes, each of the 



