DISEASES OF THE PHARYNX AND (ESOPHAGUS. 
161 
kinds of animals, it will be considered separately in each. The obstiac¬ 
tive bodies are divisible into two classes :—( a ) Wound-producing foreign 
bodies which pierce the mucous membrane, and remain in position in 
consequence of their rough surface; and (b) mere mechanical obstructions 
which, on account of their size, are unable to pass through the tube. 
The first are most frequently found in the pharynx, the lattei in the 
oesophagus, though the first variety are also met with here. 
According to Rubeli’s experiments, the striped muscular fibres, which in 
man are confined to the first two-thirds of the oesophagus, are m animals 
continued almost to the stomach. In ruminants the oesophagus possesses no 
unstriped muscular tissue whatever. This first appears in the lumen. n 
all animals the mucous membrane is invested with a thick stratified epithelium, 
covered with numerous papillae, and the mucosa possesses lymph lol he es 
together with mucous glands. The area of the oesophageal tube stanc s m 
inverse proportion to the strength of its muscular coat. In the legion o ie 
cardiac opening a thickening and narrowing occur in all domesticated 
animals, with the exception of cattle and dogs. 
The oesophagus of the horse is absolutely and relatively the longes , u 
also the narrowest. According to Franck, its length is nearly 49 inches. 
Rubeli found it to be from 50 to 52 inches, measured in position, and m 
larger animals even 56 to 60 inches. Its walls are strong, and become so 
much thicker between the diaphragm and the cardiac opening that the lumen 
of the tube almost entirely disappears, explaining the frequent occurrence m 
this region of diverticula, stenoses, and obstructions. . 
The oesophagus of ruminants and carnivora is more cylindrical. In oxen a 
contraction occurs at the lower end of the upper third, and from this pom 
onwards the diameter increases, while the wall is comparatively thin, and 
decreases in strength from above downwards. 
In sheep the thickness increases from below upwards, but the muscu ai 
wall is very thin in comparison with the surface of the mucous membrane. 
The narrowing at the middle of the oesophagus, remarked m the goat, is 
wanting in the sheep. . . , , , ■ 
Swine have also a contraction at the middle of the tube, which from this 
point enlarges both above and below. In dogs the narrowest point lies at the 
height of the lower portion of the cricoid cartilage, the width being about 
If inches. The tube increases from here to a circumference of 2 4 nicies, 
then narrows to 2 inches, dilates for a second time, and, about 6 niches 
behind the pharynx, attains a circumference of 3 inches. The last contraction, 
some 2f inches in front of the cardia, measures 2J inches. From here the 
oesophagus widens like a funnel, until it enters the stomach (the figures le ei 
to the width of the mucous membrane). , . 
In cats two contractions exist: the upper lies j inch behmd the pharynx, 
the lower at the point where the oesophagus pierces the diaphragm. q 
latter is the more distinct, the circumference only measuring about 2 lines. 
The views with regard to the mechanism of swallowing are very varied. 
It was formerly believed that the masticated food was advanced by peristaltic 
movements of the oesophagus, but Kronecker and Meltzer have ascribed this 
duty to the muscles of the pharynx, especially the broad hyoid by which the 
soft fluid nourishment is injected into the stomach. Hard substances, as 
well as any materials remaining in the pharynx are passed forward by le 
constrictors. The process is a reflex act produced by stimuli from the glosso¬ 
pharyngeal nerve and transmitted by the superior laryngeal (Wasiheil). 
