Page 290 - Clinical Anatomy

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The tongue and floor of the mouth 275

Nerve supply

The anterior two-thirds of the tongue receives its sensory supply from the
lingual branch of V which also transmits the gustatory fibres of the chorda
tympani (VII).
Common sensation and taste to the posterior one-third, including the
vallate papillae, are derived from IX. A few fibres of the superior laryngeal
nerve (X) carry sensory fibres from the posterior part of the tongue.
All the muscles of the tongue except palatoglossus are supplied by XII;
palatoglossus, a muscle of the soft palate, is innervated by the pharyngeal
branch of X.

Development (Fig. 199)

Asmall nodule, the tuberculum impar, is the first evidence of the developing
tongue in the floor of the pharynx. This is soon covered over by the lingual
swellings, one on each side, derived from the first branchial arch. These fuse
in the midline to form the definitive anterior two-thirds of the tongue sup-
plied by V and reinforced by chorda tympani.
Posteriorly, this mass meets the copula (or hypobranchial eminence), a
central swelling in the pharyngeal floor which represents the 2nd, 3rd and
4th arches and which forms the posterior one-third of the tongue (nerve
supply IX and X).
The tongue muscles derive from the occipital myotomes which migrate
forward dragging with them their nerve supply (XII, the hypoglossal
nerve).

Fig. 199◊Development of the tongue.