xm 



PHYLUM CHORDATA 



387 



(cerv. a. s.) placed 

 at the root of the 

 neck. Each side of 

 the interclavicular 

 gives off an axillary 

 air-sac, lying in the 

 arm-pit. All these 

 sacs are paired ex- 

 cept the inter- 

 clavicular, which is 

 formed by the 

 fusion of right and 

 left moieties. The 

 sacs are in com- 

 munication with the 

 pneumatic cavities 

 of the bones. 



The ventral or 

 free walls of the 

 thoracic air-sacs of 

 each side are 

 covered by a sheet 

 of fibrous tissue, 

 the oblique septum 

 (obi. sept.), which is 

 continued forwards 

 to the pericardium, 

 and is united with 

 its fellow of the 

 opposite side in the 

 middle dorsal line : 

 it divides the cce- 

 lome into two com- 

 partments one 

 containing the lungs 

 with the interclavi- 

 cular and thoracic 

 air-sacs, the other 

 (abd. cav.) the heart, 

 liver, stomach, in- 

 testine, &c., with 

 the abdominal air- 

 sacs. 



Besides the 

 branches to the 

 air-sacs, the main 

 bronchus gives 



