The Microscope. 366 



As before, this can be seen by removing the superficial fibres. In 

 the 8-12 cm. next to the stomach, the ectal fibres become more 

 nearly perpendicular to the longitudinal axis of the oesophagus, 

 while the ental fibres retain the former inclination of about 45°. 



Sheep. — In the sheep, where regurgitation is a normal and fre- 

 quent act, it might be supposed that there would be a well -developed 

 longitudinal layer of muscle, but such is not the case. Even the 

 longitudinal bands found in the horse and hog are not present. The 

 muscular fibres form two oppositely directed spirals, which cross one 

 another on the dorsal and ventral walls. Both lines of decussation 

 are quite well marked. Throughout the length of the tube the 

 ectal fibres are only slightly inclined, but as soon as they become 

 ental, their angle of inclination increases in the cephalic third to 

 65*^, decreasing to •45'^ in the middle third, after which the ental and 

 ectal fibres assume approximately the same angle with the meson — 

 abou.t 45° — and thus meet each other at a right angle. In the last 

 2-5 cm. the ectal fibres become almost longitudinal before extend- 

 ing upon the stomach. 



At many places in the length of the oesophagus small offshoots 

 take their origin from an otherwise regular bundle of fibres. 

 These offshoots pursue an irregular course, sometimes extending 

 longitudinally for a few centimeters, and then dipping down and 

 continuing in the regular course, or they may simply be inclined at 

 a different angle fi-om the other fibres of the layers. 



Ox. — The disposition of the muscular fibres in this animal is 

 very similar to the arrangement found in the sheep, but there are 

 some constant differences. In the pharyngeal third it looks as 

 though the fibres regularly encircled the oesophagus, but by remov- 

 ing the superficial layers upon the dorsal and ventral walls, the lines 

 of decussation can be seen. The ental fibres in the pharyngeal third 

 have an inclination from the longitudinal axis of about 30*-*. As 

 soon, however, as they cross and become ectaJ, they assume a direc- 

 tion nearly perpendicular to the axis. As the ectal fibres 

 approach the line of decussation, some, instead of passing under the 

 bands from the other layer, pass over, and thus cover the crossing 

 place. It is to this fact that the annular appearance is due. Con- 

 tinu.ing toward the stomach, the ectal fibres become less inclined to 

 the axis, while the inclination of the ental fibres increase, so that at 

 the junction of the middle and gastric thirds, each layer has an 

 inclination of about 45°, and thus continue to the stomach. 



As with the sheep, there are irregularities in places, and these 

 are of much the same nature as in the sheep. Longitudinal bands 



