450 THE DIGESTIVE APPARATUS IN MAMMALIA. 



muscles ; but it becomes white, like the involmitary fibres, after the tube 

 enters the mediastinum, and acquires cousiderable thickness and marked rigidity 

 in the dead animal. It is to be noted that this arrangement of the muscular 

 tunic is especially evident towards the insertion of the oesophagus into the 

 stomach, and that the muscular tube is at this point so narrow, that it is almost 

 exactly occupied by the folds of mucous membrane it contains. For this reason 

 it is that, in this state of cadaveric rigidity, we may inflate a stomach by the 

 pylorus without applying a ligature to the oesophagus ; the aperture of the 

 canal being so perfectly closed that it does not allow a bubble of air to escape. 

 In describing the interior of the stomach, we will refer to the consequences 

 resulting from this interesting anatomical fact. 



Vessels and nerves. — The oesophagus is supplied with blood by the divisions 

 given off by the common carotid artery, as well as the bronchial and oesophageal 

 arteries. The nerves are almost exclusively derived from the pneumogastric ; 

 the motor nerves are the superior oesophageal filaments — branches of the 

 external pharyngeal and laryngeal ; the sensitive filaments are derived from 

 the recurrent nerve. For the portion beyond the heart, the sensitive-motor nerves 

 are supplied by the oesophageal nerves of the pneumogastric, though in an 

 asymmetrical manner. 



Functions. — This canal conveys nutriment from the pharynx to the 

 stomach ; it has no other uses. 



Differential Characters of the (Esophagus in the other Animals. 



In all the other domesticated animals, the muscular coat is red-coloured throughout its 

 whole extent, and everywhere offers the same degree of thickness and the same flaccidity. The 

 canal is also as wide towards the stomach as at the pharynx. In Rdminants and the Car- 

 NivoRA, it enters the stomach as a funnel-shaped (infundibuliform) tube. 



In the Camel, the mucous membrane adheres more closely to the muscular tissue than in 

 Solipeds, according to Colin. 



The dilatability of the oesophagus is very remarkable in these animals : Dogs swallow large 

 pieces of flesh ; and Cows and Oxen are able to ingest large turnips, or such voluminous foreign 

 bodies as shoes. 



(In Ruminants and the Carnivora the oesophagus is, proportionally^, wider than in the 

 Horse and Pig.) 



Comparison of the (Esophagus of Man with that of Animals. 



The oesophagus of Man resembles that of Carnivora; its diameter is almost uniform. It 

 also inclines to the left below the neck, but in the thorax is in the median line, though it again 

 deviates to the left as it joins the stomach. As the thyroid in Man is very voluminous, it is 

 related to the oesophagus in the upper part of the neck. Two small accessory fasciculi, belong- 

 ing to the muscular tunic of the oesophagus, have been described : one is the broncho- oesophageal 

 muscle, which is detached from the left bronchus; and the other the pleuro -oesophageal muscle, 

 detached from the left layer of the posterior mt diastinum. 



Article II.— The Essential Oegans of Digestion. 



These organs being all contained in the abdominal cavity, this common 

 receptacle will first be studied ; afterwards the sfomach, intestines, and their 

 annexed organs — the liver, pancreas, and spleen — will be described. 



The Abdominal Cavity. 



In Mammalia, the interior of the trunk is partitioned by the diaphragm 

 into two great cavities, which lodge the majority of the organs so vaguely 



