MUSCULAR COAT. 509 



The (Esophagus is very muscular ; its longitudinal fibres are con- 

 tinuous above with the pharynx, and are attached in front to the 

 vertical ridge on the posterior surface of the cricoid cartilage ; the 

 uppermost circular fibres are also attached on each side to the 

 cricoid cartilage. Below, both sets of fibres are continued upon 

 the stomach. On the stomack the longitudinal fibres are most appa- 

 rent along the lesser curve, and the circular at the smaller end. At 

 the pylorus the latter are aggregated into a thick circular ring, 

 which, with the spiral fold of mucous membrane, constitutes the 

 pyloric valve. At the great end of the stomach a new order of 

 fibres is introduced, having for their object to strengthen and com- 

 press 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, equally distri- 

 buted over the entire surface. At the termination of the ileum the 

 circular fibres are continued into the two folds of the ilio-caecal 

 valve, while the longitudinal fibres pass onwards to the large intes- 

 tine. In the large intestine the longitudinal fibres commence at 

 the appendix vermiformis and are collected into three bands, an 

 anterior, broad; and two posterior and narrower bands. These 

 bands are nearly one half shorter than the intestine, and give to it 

 the sacculated appearance which is characteristic of the cascum 

 and colon. In the descending colon the posterior bands usually unite 

 and form a single band. From this point the two bands are con- 

 tinued downwards upon the sigmoid flexure to the rectum, around 

 which they spread out and form a thick and very muscular lon- 

 gitudinal layer. The circular fibres in the caecum and colon are 

 exceedingly thin ; in the rectum they are thicker, and at its lower 

 extremity they are aggregated into the thick muscular ring which 

 is called the internal sphincter ani.* 



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. 



The Stomach is completely surrounded, by the peritoneum ex- 

 cepting along the line of junction of the great and lesser omentum. 

 The first or oblique portion of the duodenum is also completely in- 



* Mr. Wilson does not seem to have paid the same close attention to the anatomy of 

 the anus as to other parts of the body, and we here find a deficiency in the description 

 which we shall endeavour to supply. 



The Muscular coat of the rectum consists of much stronger fasciculi than that of 

 the colon ; the transverse fibres terminate at the anus by aggregating into a ring which 

 is called the internal sphincter muscle, as in c fig. 152. The longitudinal fibres being 

 outside of the transverse, when they reach the internal sphincter wind around it and 

 are inserted into the submucous coat from one to four inches above the anus. They 

 thus form a pulley-like arrangement which everts the mucous membrane in defecation 

 and is the active agent in producing prolapsus ani. I have observed that when haemor- 

 rhoids exist many of the fibres run to be inserted into them, hence their ready extru- 

 sion when the patient is directed to force them down. The following cut exhibits this 

 arrangement. See Hornet's Special Anatomy, 1836. G. 



