186 DIGESTION. 



various glands situated beneath it and in its substance, which 

 have already been described, presents some peculiarities, 

 which are interesting more from an anatomical than a physi- 

 ological point of view. In the superior portion, which forms a 

 cuboidal cavity just behind the posterior nares, the membrane 

 is darker and much richer in blood-vessels than in other 

 parts. Its surface is smooth and provided with ciliated col- 

 umnar epithelium, like that which covers the membrane of 

 the posterior nares. It is marked by a deep antero-posterior 

 groove in the median line ; and on either side, parallel with 

 the median line, are four smaller grooves. In the horizontal 

 portions, the mucous membrane in the central groove adheres 

 to the periosteum of the basilar process, particularly at its 

 posterior extremity. Laterally, below the level of the open- 

 ing of the Eustachian tubes, and posteriorly, at the point where 

 it becomes vertical, the mucous membrane abruptly changes 

 its character. The epithelial covering is here composed of 

 cells of the pavement variety, similar to those which cover 

 the mucous membrane of the oesophagus. The membrane is 

 also paler, and is less rich in blood-vessels. It is provided 

 with papillae, some of which are simple conical elevations, while 

 others are split into from two to six conical processes with a 

 single base. These papillae are rather thinly distributed over 

 the whole of that portion of the mucous surface which is cov- 

 ered with pavement epithelium. 



The contractions of the muscular walls of the pharynx 

 force the alimentary bolus into the oesophagus, a tube pos- 

 sessed of thick muscular walls, extending to the stomach. 

 The oesophagus is about nine inches in length. It is cylin- 

 drical, and rather constricted at its superior and inferior ex- 

 tremities. It commences in the median line behind the 

 lower border of the cricoid cartilage and opposite the fifth 

 cervical vertebra. At first, as it descends, it passes a little 

 to the left of the cervical vertebrae. It then passes from left 

 to right from the fourth or fifth to the ninth dorsal vertebra, 

 to give place to the aorta. It finally passes a little to the 



