MUSCULAR COAT. 



513 



Fig. 224.-J- 



by a zone or wreath of simple follicles. When opened, they are seen to 

 consist of a small flattened saccular cavity, containing a mucous secretion, 

 but having no excretory duct. They are chiefly found in the lower part 

 of the ileum. The solitary glands of the large intestine are most abundant 

 in the caecum and appendix cseci ; they are small circular prominences, 

 flattened upon the surface, and perforated in the centre by a minute ex- 

 cretory opening. 



The Aggregate, or Peyer's* glands, are situated near the lower end of 

 the ileum, and occupy that portion 

 of the intestine which is opposite the 

 attachment of the mesentery. To 

 the naked eye they present the ap- 

 pearance of oval disks, covered with |f 

 small irregular fissures ; but with the 

 aid of the microscope they are seen 

 to be composed of numerous small 

 circular patches, surrounded by sim- 

 ple follicles, like the solitary glands 

 of the small intestine. Each patch 

 corresponds with a flattened and 

 closed sac, situated beneath the 

 membrane, but having no excretory 

 opening, and the interspace between 

 the patches is occupied by flattened 

 villi. 



The Simple follicles, or follicles of Lieberkiihn,* are small pouches of 

 the mucous layer, dispersed in immense numbers over every part of the 

 mucous membrane. 



MUSCULAR COAT. The muscular coat of the pharynx consists of five 

 pairs of muscles, which have been already described. The muscular coat 

 of the rest of the alimentary canal is composed of two planes of fibres, an 

 external longitudinal, and an internal circular. 



The (Esophagus is very muscular ; its longitudinal fibres are continuous 

 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 to the cricoid cartilage. Below, both sets of fibres are 

 continued upon the stomach. 



Besides the fibres possessed by the esophagus in common with the rest 

 of the alimentary canal, two special muscles have been described by Hyrtl 

 under the names of Broncho-oesophageal and Pleuro-oesophageal. The 

 Broncho-cesophageal muscle arises as a broad fasciculus from the posterior 

 surface of the left bronchus, and is lost, after a course of two or three 

 inches in length, among the longitudinal fibres of the left side of the ceso- 

 phagus. The Pleuro-O2sophageal muscle arises from the left wall of the 

 posterior mediastinum behind the commencement of the descending aorta, 

 and curves around that vessel to mingle its fibres with the longitudinal 

 fibres of the oesophagus. 



* John Conrad Peyer, an anatomist of Schaffhausen, in Switzerland. His essay, "IV 

 Glandulis Intestinorum," was published in 1677. 



j- Portion of one of the patches of Peyer's glands from the end of the ileura,: 

 magnified. The villi are also shown. (5o^m.) 



2H 



