514 



SEROUS COAT. 



Fig. 225* 



On the Stomach the longitudinal fibres are most apparent along the 

 lesser curve, and the circular at the smaller end. At the pylorus the latter 

 are aggregated into a thick circular ring, \vhich, with the spiral fold of 

 mucous membrane found in this situation, constitutes the pyloric valve. 

 At the great end of the stomach a new order of fibres is introduced, hav- 

 ing for their object to strengthen and compress that extremity of the organ. 

 They are directed more or less horizontally from the great end towards 

 the lesser end, and are generally lost upon the sides of the stomach at 

 about its middle ; these are the oblique fibres. 



The Small intestine is provided with both layers of fibres, equally dis- 

 tributed over the entire surface. At the termination of the ileum the cir- 

 cular fibres are continued into the two 

 folds of the ileo-csecal valve, while the 

 longitudinal fibres pass onwards to the 

 large intestine. In the large intestine 

 the longitudinal fibres commence at 

 the appendix vermiformis and are col- 

 lected into three bands, an anterior, 

 broad, and two posterior and narrower 

 bands. These bands are nearly one- 

 half shorter than the intestine, and 

 serve to maintain the sacculated struc- 

 ture which is characteristic of the 

 ., caBcum and colon. In the descending 

 colon the posterior bands usually unite 

 and form a single band. From this 

 point the bands are continued down- 

 wards upon the sigmoid flexure to the 

 rectum, around which they spread out 

 and form a thick and very muscular 

 longitudinal layer. The circular fibres 

 in the caecum and colon are exceed- 

 ingly thin ; in the rectum they are 



thicker, and at its lower extremity they are aggregated into the thick mus- 

 cular ring which is know r n as the internal sphincter ani. Between the 

 latter and the mucous membrane are several narrow fasciculi of longitudi- 

 nal muscular fibres, somewhat more than an inch in length, which have 

 been described by Horner of Philadelphia. 



SEROUS COAT. The pharynx and oesophagus have no covering of 

 serous membrane. The alimentary canal within the abdomen has a serous 

 layer, derived from the peritoneum. 



* A vertical section of the parietes of the anus, passing through the middle line of 

 one of the columns of the rectum, and the neighbouring parts. 1. The internal sphincter, 

 with its arched fibres transversely divided. 2. 2. The plane of arched fibres of the 

 muscular coat, similarly divided. 3. The point of greatest contraction of the internal 

 sphincter. 4. The external sphincter. 5. The point of greatest contraction of the ? rtine 

 muscle. 6. The plane of longitudinal fibres of the muscular coat, longitudinally divided. 

 7. Some of these fibres terminating in the internal sphincter. 8. Others, terminating in 

 the external sphincter. 9. The remaining longitudinal fibres, collected into a semiten- 

 clinous fasciculus, passing over the lower margin of the internal sphincter, to be reverted 

 jpward within the duplicature of the column. 10. These reverted fibres again becom- 

 ing muscular, and terminating in the mucous coat. 11. The mucous coat. 12. A bristle 

 >n one f f the sae-s. G. \ 



