PHYLUM CHORDAfA 



453 



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

 Krause, after Schneider.) 



cent 



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 A 

 of the larynx are, in addition f-X'^ 



to the epiglottis, which has ^i-r^Lx? 

 been'j already referred to |: ' \-ih 

 (p. 448), the large thyroid \\wmf 

 (th.), which forms the ventral 



and lateral walls, the ring-like *^ ^ 



cricoid (cr.), the two small 

 arytenoids (ary.), and a pair FlG . no3.-i.epus cunicuius. Larynx. A. 

 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 

 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- 

 no. iio4.-i.epus cunicuius. Diagram of a siderable interval owing to 



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

 ventricles to show the relations of the pleurae, media- ^.'j-' i~ J.T_ * 



stinum, etc. The lungs are contracted, aorl. dorsal partition between them OI 



aorta; az.v. azygos vein; cent, centrum of thoracic fl cnppp flip rnprlificfinnrn 



vertebra; Ling, left lung; l.pl. left pleural sac; bp^e, t meaiaSLinum, 



l.vent. left ventricle ; my. spinal cord ; ces. oeso- in which as alreadv CX- 

 phagus ; par. per. parietal layer of pericardium ; pt. , . , ,'. , , > 



cav. post-caval, close to its entrance into right auricle ; plained, lie the heart and 



r.lng. right lung j7vpZ.rightpleur.il cavity ; r. vent, right ~fi, 01 . riT , fTQT , Tli lv,r 



ventricle ; st. sternum ; v.med. ventral mediastinum. <- tner organs. ne lung IS 



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 



aort 



oes 



l.ln 



