582 ROBERT MATHESON 



The tracheal supply of the fore-gut 



The distribution of the tracheae to the ahmentary canal may be 

 readily seen in figure 1. From the second and third abdominal 

 tracheal gills there arise, just previous to their union with the longi- 

 tudinal trunks, two comparatively large branches which go directly 

 to the fore-gut. The branch (6, fig. 1) from the second tracheal 

 gill first divides into two to five branches which, with their many 

 ramifications, supply the anterior portion of the gizzard and 

 oesophagus. However, there is much variation in the distribution 

 of the tracheal supply in different individuals. In some (fig. 1, h) 

 the first branch breaks up into two branches each of which finally 

 divides into a large number of smaller tracheae distributed over 

 the anterior portion of the gizzard while one small branch {tr, 

 fig. 2) runs forward along the side of the oesophagus giving off to 

 it numerous small tracheae. This seems to be the more common 

 method of distribution of this trunk. If, however, figure 2 be 

 examined, it is easily seen how greatly modified this may be. 

 Here the first tracheal trunk, h, divides into five branches, the 

 posterior one of which is distributed over the caudal portion of 

 the gizzard while the remainder furnish the usual tracheal supply 

 to the oesophagus and gizzard. Even in the same individual 

 the branching and distribution of this trunk varies considerably^ 

 on the opposite sides. 



The second tracheal trunk (c) arises from the third abdominal 

 gill (fig. 1, 3 ah). It divides just before reaching the intestine 

 into two branches. The posterior branch supplies the ventral 

 caecum as seen on the right side of figure 1 . The anterior branch 

 passing forward on the ventral side of the caeca breaks up into 

 five small branches, each of which in turn divides into numerous 

 smaller branches. These furnish the tracheal supply of the pos- 

 terior portion of the gizzard and that portion of the alimentary 

 canal between it and the mid-gut. There is considerable varia- 

 tion in the branching and distribution of this trunk even on the 

 opposite sides of the same individual. On the left side of figure 

 1 it may be seen that the large trunk coming from the tracheal 

 gill gives off two branches instead of one to the ventral caecum. 



