Floor of Mouth Anatomy
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Direct answer
Nothing in the oral cavity is more crowded per square centimetre than the floor of the mouth — a shallow trough between the ventral tongue above and the mylohyoid sling below, carrying the sublingual glands, the submandibular ducts, the lingual nerves with the submandibular ganglia, the hypoglossal nerves and the deep lingual veins, all under a thin mucosa whose midline fold is the lingual frenulum. The mylohyoid muscle is the organising structure: it divides the sublingual space (above) from the submandibular space (below), and the posterior free edge of mylohyoid is the gate through which the two spaces — and their infections — communicate. Each submandibular (Wharton's) duct runs forward from the deep lobe of the gland, opens at the sublingual caruncle beside the frenulum, and is crossed twice by the lingual nerve, which loops under and then back over it.
What you must remember
- The platform: mylohyoid from the mylohyoid line of the mandible to a midline raphe and the body of the hyoid; supplied by the mylohyoid nerve (V3); geniohyoid lies above it, digastric below.
- Sublingual gland: smallest of the major glands, sits in the sublingual fossa above mylohyoid; predominantly mucous; drains by 8-20 ducts of Rivinus directly into the floor, with the largest (Bartholin's duct) often joining Wharton's duct.
- Submandibular duct: about 5 cm, from the deep lobe, passes forward between mylohyoid and hyoglossus, opens at the sublingual caruncle — the site to milk for pus in sialadenitis and to cannulate for sialography.
- Nerve relations: the lingual nerve crosses Wharton's duct twice — under it, then over it — carrying general sensation of the anterior tongue plus chorda tympani fibres; the submandibular ganglion hangs from the lingual nerve here; the hypoglossal nerve runs below the duct on hyoglossus to the tongue muscles.
- Vessels: lingual artery (from the external carotid, entering the tongue at the posterior border of hyoglossus — located within Pirogoff's triangle) and the deep lingual (ranine) veins visible beside the frenulum.
- Surface landmarks: lingual frenulum midline, sublingual caruncles on either side, plica sublingualis with the gland bulging under it, fimbriated folds lateral to the frenulum.
- Clinical anchors: ranula (a bluish translucent swelling of the sublingual region from duct leakage), ankyloglossia of a tight frenulum, and Ludwig's angina arising when sublingual and submandibular spaces swell together.
A ranula, followed layer by layer
A translucent blue swelling in the floor of the mouth of a teenager, pushing the tongue up, is the standard clinical entry into this anatomy — and dissecting it layer by layer earns the marks. The mucosa bulges over the plica sublingualis; beneath it the sublingual gland or a torn duct of Rivinus has leaked mucus into the loose sublingual connective tissue above mylohyoid, forming a mucocoele that glistens like a frog's belly — hence ranula. Now the surgical anatomy decides options: simple marsupialisation, excision of the gland itself through an intraoral approach, or, when the swelling plunges below mylohyoid around its posterior free edge into the submandibular space (a plunging ranula), a combined cervical approach. The neighbouring structures set the risks — the lingual nerve and Wharton's duct must be identified and preserved in the floor, and the hypoglossal nerve deeper along hyoglossus guarded. Every step of that plan is this topic's anatomy applied in order.
Where marks are lost
Two slips dominate. First, the double crossing of Wharton's duct by the lingual nerve — asked directly in viva as "which structure crosses the submandibular duct twice?" — is written in reverse (it is the nerve that loops, first below and then above, so the duct ends up medial to the nerve at the caruncle). Second, the mylohyoid's role as the dividing wall: infection of a mandibular second or third molar, whose roots lie below the mylohyoid line, presents as a submandibular (neck) swelling, whereas premolar and incisor infections present in the mouth — the single most useful clinical sentence in the topic and a fixture of Indian oral surgery vivas.
Frequently asked questions
Which muscle forms the floor of the mouth?
Mylohyoid, supplemented anteriorly by geniohyoid; it separates the sublingual space above from the submandibular space below.
Where does Wharton's duct open?
At the sublingual caruncle, a papilla beside the base of the lingual frenulum, after being crossed twice by the lingual nerve.
What is a ranula?
A mucus extravasation phenomenon of the sublingual gland region presenting as a translucent bluish floor-of-mouth swelling; it plunges below mylohyoid when it herniates through the muscle's posterior free edge.
What is Pirogoff's triangle and its use?
The triangle between the hypoglossal nerve, the intermediate tendon of digastric and the posterior border of mylohyoid — a guide to ligating or locating the lingual artery in the floor of the mouth.
Why does a lower molar abscess present as a neck swelling?
Because the molar roots lie below the mylohyoid line, so pus tracks into the submandibular space rather than the sublingual space.