198 The Alligator and Its Allies 



until long after hatching. In the genus Alligator 



the trachea is straight. 



More universal than this 

 looped structure there is found 

 another peculiar structure in 

 the crocodilian trachea. It 

 is a short vertical partition in 

 the stem just before its divi- 

 sion into the two branches. 

 This partition is partly mem- 

 branous and possesses one or 

 more stiffening cartilaginous 

 strands which are outgrowths 

 of so many cartilaginous rings 

 of the trachea. The number 

 of the stiffening fibers varies 

 in the different species. 



The number of the tracheal 

 rings varies not only in the 

 different species but also in 

 different individuals of the 

 same species. There are be- 

 tween fifty and sixty in A. 

 mississippiensis. According 

 to Rathke the number of rings 

 in the individual animal al- 

 most certainly does not in- 

 crease with age. The number of rings is smallest 

 in the gavials and greatest in the crocodiles (genus 

 Crocodiliis). The number of rings in the two 



Fig. 57. Respiratory 

 Organs. 



b, bronchus: e, oesophagus; g, 

 glottis; /, lung; t, tongue; /;•, 

 trachea. 



