214 Mr Harrison, A preliminary account of the 
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dilatator muscles are inserted into the pharyngeal walls, the right 
and left dorsal, lateral, and ventral dilatators of the pharynx (rdd., 
rvd.). The dorsal pair are inserted dorso-laterally into the pharyn-— 
geal wall, and pass upwards, and slightly outwards and forwards, — 
to attach to the wall of the head close to the mid-line. The lateral — 
pair run outwards, and slightly upwards and backwards, to be 
inserted into the head-wall immediately above the eyes. The © 
ventral pair run downwards, outwards, and slightly backwards, to — 
be inserted into the head-wall midway between the eye and the — 
mid-ventral line. This muscle is thus considerably displaced in 
Fig. 1 of Plate VII, which has been slightly schematised for the 
sake of clearness. Immediately behind these dilatator muscles a 
posterior sphincter (psp.) occurs; and behind this a pair of posterior 
dorsal dilatators (rpdd.), which have the same relations as the 
anterior pair. Pawlowsky attaches the ventral dilatators behind 
the posterior sphincter, but they are inserted between the sphincters 
in the same plane as the dorsal and lateral dilatators. 
ivd. 
} lab.? 
Fig. 6. Transverse section through pharynx and diverticulum at 
level of eyes. Diagrammatic. 
The function of the pharynx would appear from its musculature 
to be twofold. Contraction of the sphincters closes the cavity, and 
allows of the production of a partial vacuum in the pumping- 
pharynx. Simultaneous dilatation of the pharynx and relaxation 
of the roof of the pumping-pharynx causes the blood to pass from 
the latter chamber to the former. The next contraction of the 
sphincters, and it seems probable here also that the anterior 
sphincter contracts first, forces the blood into the gullet. 
The oesophagus is a narrow tube passing downwards from the 
posterior end of the pharynx between the brain and sub-oesophageal 
en 
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