The Microscope, 367 



2. These layers cannot be designated longitudinal and circular. 

 8. These layers cannot be designated ectal and ental. 

 •4. Fibres that are on one side ectal are on the other ental, and 

 vice versa. 



5. If longitudinal and circular layers exist with any regularity, 

 it is only in the gastric end of the tube. 



6. The typical arrangement may be thus described. In the 

 walls of the oesophagus there are two layers of muscle fibres, 

 arranged in spirals. These spirals are wound in opposite directions 

 around the tube. Upon the dorsal and ventral walls they cross 

 each other, by dividing into small bundles which interdigitate, the 

 ectal becoming ental, and the ental, ectal. 



MICROSCOPIC ANATOMY. 



[The following discussion does not refer to the muscularis 

 mucosce.^ 



The first feature that impresses one upon making a microscopic 

 examination of the muscle of the oesophagus is, that in some of the 

 domesticated animals a part of the tissue is composed of striated, 

 and a part of unstriated fibres. In brief, the relations of the two 

 kinds of muscles are as follows: 



In the horse, non-striated fibres begin with the gastric third 

 and increase in number approaching the stomach, but a few striated 

 fibres continue to the stomach.* 



In the pig, non- striated fibres begin to appear 12-18 cm. 

 from the gastric extremity, and increase is number to the stomach, 

 but, as before, some striated fibres continue to the stomach, and in 

 this case are much more abundant. 



In the sheep, ox and dog, no non- striated fibres are found 

 cephalad of the diaphragm. 



In the cat, when the ectal fibres first become longitudinal, the 

 non-striated fibres begin to appear, and soon they alone are found. 

 In the ental or circular portion, the non-striated fibres appear at the 

 same level and sooner exclude the striated. 



TERMINATIONS OF FIBRES. 



In every oesophagus examined, fibres gradually tapering to a 

 point were found. They were present in nearly all of the prepara- 

 tions examined, showing this to be an exceedingly common method 

 of ending. Near the end of the fibre there is a marked swelling, 

 and at this point a large nucleus. Just before making this expan- 



*This was true of the only horse's cesophagus examined microscopically. 



