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 somany 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 
Fic. 57, _ResriRaToRY to Rathke thenumber of rings 
i heenehuse & esophhgnes y 1: The amdividual animal ‘al- 
Bethea," Agi fongues ost certainly does not in- 
crease with age. The number of rings is smallest 
in the gavials and greatest in the crocodiles (genus 
Crocodilus). The number of rings in the two 
