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THE AMERICAN NATURALIST [Vol. XL 



cartilages of the pectoral girdle from the ventral side of the throat. 

 It is of a whitish color, and its walls are tough and thick. Anteri- 

 orly it divides to form the arterial arches of each side, and posteri- 

 orly it narrows suddenly to form the truncus, which connects with 

 it at somewhat of an angle, instead of entering exactiv ui the middle 

 line. Its ventral surface is smooth and even, while its dorsal sur- 

 face may l)e more or less grooved longitudmalK-, as seen in the 

 hgure. In cross section it is cUipticnl, and is coin pressed in a 

 dorso-vcntral direction. 



