34 Anatomy, Physiology, and Patlioloyy of the 
of two orders of fibres, which partly decussate on each side of 
the canal, the internal layer thus becoming the ex- 
ternal, and vice versa; their leading arrangement 
may, however, be compared to two circular- shaped 
bands placed obliquely, the one within the other, 
by which an equal facility is given to their ac- 
tion when commencing at either extremity. In its 
course down the neck, the oesophagus is situated 
more above the trachea than in the horse, it passes 
between the two first ribs, traverses the upper 
part of the chest, penetr.ates an opening in the dia- 
phragm (midriff) termed the foramen sinistrum, and enters the 
anterior and superior portion of the rumen. At the lower end of 
the tube the outer order of muscular fibres is found to take a 
direction nearly parallel with its course, and to be reflected upon 
the rumen, blending with the external muscular layer of that 
viscus. (See a. Jig. 4.) The mucous lining membrane, to which 
we have before referred, lies in longitudinal plaits in a passive 
state of the oeosphagus ; an arrangement which allows of its being 
extended in the ascent or descent of the ingesta, for it is very 
loosely joined to the muscular coat. Between these two coats a 
considerable quantity of elastic tissue exists, which throws the 
membrane into the above-named folds after being upon the stretch, 
for of itself it is devoid of contractility and elasticity. 
We proceed to a description of the stomachs. The size, shape, 
entrance into, and passage out of the stomach are modified ac- 
cording to the nature of the food and the habits of the animal. 
As before observed, the organ possesses its simplest form in the 
carnivora, and its most complicated in the ruminantia. In vege- 
table feeders it is always more complex than in those animals 
that subsist on flesh, as a necessity exists for the aliment to be 
detained within it for a greater length of time. We have good 
evidence of this by comparing the stomach of the dog with that 
of the horse; in the former, the openings leading to and from the 
cavity are far removed, while in the latter they are situated close 
to each other ; hence the ingesta has to travel nearly to the place 
where it entered before it can escape. This causes a longer re- 
tention and a more complete action of the gastric juice upon the 
ingesta, to prepare it for conversion into blood. In omnivorous 
animals, as the pig, the stomach is imperfectly divided into two 
or more compartments or pouches, an arrangement which allows 
certain qualities of food to be kept within it for a longer period. 
We should also mention, that in the omnivora the mucous mem- 
brane of the oesophagus lines a small portion of the cardiac orifice 
of the organ ; in the carnivora it ends immediately at the en- 
trance of the tube ; but even in the simple- stomached herbivora 
