72 COMPARATIVE ZOOLOGY. 
backward, and by a glairy juice, called saliva, which fa- 
cilitates its passage through the gullet.” Vertebrates have 
a cavity behind the mouth, called the throat, or pharynx, 
which may be considered as a funnel to the cesophagus.” 
In air-breathers, it has openings leading to the windpipe, 
nose, and ears. In Man, as in Mammals generally, the 
process of deglutition is in this wise: the food, masticated 
by the teeth and lubricated by the saliva, is forced by the 
tongue and cheeks into the pharynx; the soft palate keep- 
ing it out of the nasal aperture, and the valve-like epiglot- 
tis falling down to form a bridge over the opening to the 
windpipe. The moment the pharynx receives the food, 
it grasps it tightly, and, the muscular fibres contracting 
above it and left lax below it, it is rapidly thrust into the 
cesophagus. Here, a similar movement (the peristaltic) 
strips the food into the stomach.” The rapidity of these 
contractions transmitted along the cesophagus may be ob- 
served in the neck of a Horse while drinking. 
Deglutition in the Serpents is painfully slow, and some- 
what peculiar. For how is an animal, without limbs or 
molars, to swallow its prey, which is often much larger 
than its own body? The Boa-constrictor, e.g., seizes the 
Fie. 85.—Skull of Boa-constrictor: 1, frontal; 2, prefrontal; 4, postfrontal; 5, basi- 
occipital; 6, sphenoid; 7, parietal; 12, mastoid; 13, alisphenoid; 17, premaxil- 
lary; 1S, maxillary; 20, nasal; 24, transverse; 25, internal pterygoid ; 34, dental, 
lower jaw; 35, 36, angular; a, tympanic; s, prenasal; v, petrosal. 
