366 The Microscope. 



may extend along the surface for a few centimetres, or some fibres 

 may take an inclination differing from that of the spirals. None 

 of these offshoots extend far, and if they belong to a regular system 

 the connection was not discovered. 



Dog. — In the dog the arrangement of the mu.scular fibres is 

 more regular and uniform throughout the length of the tube than 

 in any other animal examined. As before, two spirals are found 

 that decussate upon the dorsal and ventral walls. The lines of 

 decussation are distinct for their entire lengths. At the beginning 

 of the cesophagus the ectal fibres have an inclination of about 72"^ 

 to the longitudinal axis, but upon crossing the line of decussation 

 and becoming ental, they turn cephalad or caudad at such an 

 angle as to make their direction at right angles to that of the fibres 

 covering them. The directions of the fibres gradually become 

 equalized until both have an inclination of 45^. 



There are at the gastric end a few small bundles following a 

 course differing more or less from the regular one. These bundles 

 all pass to the stomach, and are the only signs of irregularity in the 

 tube. If transections were made at this point, and descriptions 

 based upon them alone, it would be easy to repeat Kline's error and 

 say that at the caudal end of the CBSOjihagus there are three layers of 

 muscular tissue. The so-called third layer exists only where a 

 bundle of fibres pursues an erratic course. 



Cat. — In this animal the spiral arrangement is again found, but 

 not in the entire length of the tube.' The ectal and ental first cross 

 at an angle of 150°, which gradually decreases to 90°. This 

 decrease is occasioned by the ectal fibres becoming more nearly 

 longitudinal and the ental more nearly circular. 



In the caudal one-third or two-fifths, the ectal layer becomes 

 approximately longitudinal, and the ental is circular. The two 

 layers are here in no way connected. The circular layer is not 

 spiral in character, nor are the fibres grouped into distinct rings, but 

 it is a uniform sheet encircling the caudal part of the tube. In the 

 caudal one-third, there is no crossing of fibres, which ceases, of 

 course, when the spirals become distinct from each other. 



The cesophagus of the cat is peculiar, in that the longitudinal 

 and circular plan is more largely developed than in the other 

 domestic animals. In the sheep this arrangement also exists in the 

 gastric end of the tube, but for a shorter distance. 



SUMMARY OF ARRANGEMENT OF FIBRES. 

 1. The muscular coat of the oesophagus is divided into two 

 layers. 



