Boundaries and walls
Each half of the nasal cavity is a tall, narrow space with a roof, floor, medial wall and lateral wall.
- Roof: narrow and arched. It slopes up behind the nasal and frontal bones, is flat at the cribriform plate of the ethmoid, and slopes down along the body of the sphenoid, where the sphenoid sinus opens.
- Floor: the hard palate, formed by the palatine processes of the maxillae in front and the horizontal plates of the palatine bones behind. It continues backwards as the soft palate.
- Medial wall (nasal septum): the perpendicular plate of the ethmoid above and behind, the vomer below and behind, and the septal cartilage in front.
- Lateral wall: the maxilla, lacrimal bone, ethmoidal labyrinth, inferior concha, perpendicular plate of the palatine bone and medial pterygoid plate.
The nasal bones and the frontal bone form the bony bridge above the external nose; the frontal sinus lies in the frontal bone behind the brow.
Conchae and meatuses
The superior, middle and inferior conchae (turbinates) curl down from the lateral wall and increase the surface for warming and humidifying air. The superior and middle conchae belong to the ethmoid; the inferior concha is a separate bone. The space under each concha is a meatus.
| Space | What opens into it |
|---|---|
| Spheno-ethmoidal recess (above superior concha) | Sphenoid sinus |
| Superior meatus | Posterior ethmoidal cells |
| Middle meatus | Frontal sinus via the frontonasal duct or infundibulum; maxillary sinus and anterior ethmoidal cells at the semilunar hiatus; middle ethmoidal cells on the ethmoidal bulla |
| Inferior meatus | Nasolacrimal duct, at its front end |
The olfactory mucosa lines the roof, the upper septum and the superior concha. The rest is respiratory mucosa: ciliated columnar epithelium over a rich venous plexus.
The nasopharynx behind the choanae
The nasopharynx is the part of the pharynx directly behind the nasal cavity, from the skull base to the soft palate. It stays open because its walls are bony or firmly fixed.
- Auditory tube opening: on the lateral wall, level with the inferior concha and a short distance behind it.
- Tubal ridge (torus tubarius): the rounded elevation above and behind the opening, formed by the cartilage of the tube.
- Salpingopharyngeal fold: a vertical mucosal fold running down from the ridge, over salpingopharyngeus.
- Pharyngeal recess (fossa of Rosenmüller): the slit behind the tubal ridge.
- Pharyngeal tonsil (adenoid): lymphoid tissue on the roof and posterior wall. It is largest in childhood and shrinks after puberty, so in an adult specimen it is often a small fibrous patch.
- Pharyngeal isthmus: the opening between the nasopharynx and oropharynx, between the soft palate and the posterior pharyngeal wall. The soft palate closes it during swallowing.
Blood supply and innervation
The nasal cavity has a rich arterial supply from both the internal and external carotid systems.
- Sphenopalatine artery (maxillary): the main supply to the lateral wall and septum, entering through the sphenopalatine foramen at the back.
- Anterior and posterior ethmoidal arteries (ophthalmic, from the internal carotid): the roof and upper parts.
- Greater palatine artery: the lower anterior septum, via the incisive canal.
- Septal branch of superior labial artery (facial): the front of the septum.
These vessels anastomose on the anteroinferior septum in Kiesselbach's plexus, at Little's area. Veins drain to the sphenopalatine and pterygoid plexus, the facial vein and the ophthalmic veins. The olfactory nerve (CN I) carries smell through the cribriform plate. General sensation comes from the anterior ethmoidal nerve (V1) in front and above, and from branches of the maxillary nerve (V2) through the pterygopalatine ganglion for most of the remainder. Secretomotor fibres come from the facial nerve through the greater petrosal nerve and the pterygopalatine ganglion.
Clinical relevance
The nose bleeds, leaks and blocks, and each of these has an anatomical explanation.
- Anterior epistaxis: most nosebleeds arise from Little's area and are controlled by pressure on the soft nose.
- Posterior epistaxis: from sphenopalatine branches, harder to reach, and may need packing or endoscopic ligation.
- Cribriform plate fracture: CSF rhinorrhoea, loss of smell and a route for meningitis.
- Sinusitis: the middle meatus is the common drainage pathway for the frontal, maxillary and anterior ethmoidal sinuses, so swelling there blocks all three.
- Adenoid enlargement: obstructs the choanae and auditory tubes, causing mouth breathing and glue ear in children.
- Nasopharyngeal carcinoma: often begins in the pharyngeal recess and may first present as a one-sided middle ear effusion in an adult.
On the specimen
The specimen is a sagittal section through the nose, palate and pharynx, viewed from the medial side with the septum removed.
- Orientation: the frontal and nasal bones are in front and above; the hard palate forms the floor and continues back into the soft palate.
- Superior concha: the smallest and highest concha, far back under the roof; do not confuse it with the larger middle concha below it.
- Tubal ridge or salpingopharyngeal fold: the ridge is the rounded cushion arching over the tube opening; the fold is the thin vertical ridge descending from it.
- Pharyngeal recess: the deep slit behind the tubal ridge, not the tube opening in front of it.
- Palatoglossal or palatopharyngeal fold: the palatoglossal fold runs down to the side of the tongue in front; the palatopharyngeal fold runs down the pharyngeal wall behind.