Page 399 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 384

384 The central nervous system

adjacent upper part of the septum, is thin and dull yellow in colour; it con-
tains the olfactory receptors and supporting cells. The remaining respiratory
portion is thick, vascular and moist with secretions of mucous glands; its
epithelium is ciliated.
The upper part of the nasal cavity receives its arterial supply from the
ethmoidal branches of the ophthalmic artery, a branch of the internal
carotid. The sphenopalatine branch of the maxillary artery, a terminal of
the external carotid, supplies the lower part of the cavity. Just within the
vestibule of the nose, on the anteroinferior part of the septum, it links with a
septal branch of the facial artery and it is from this zone, Little’s area, that
90% of nose-bleeds occur. The veins drain downwards into the facial vein
and upwards to the ethmoidal tributaries of the ophthalmic veins.

Clinical features

1◊◊The skin of the external nose and its surrounds contains many seba-
ceous glands and hair follicles which may become blocked and infected.
The significance of this fact is that the facial veins, which may become
secondarily infected, communicate directly with the ophthalmic veins and
hence with the cavernous sinus. For this reason, this zone is often known as
the ‘danger area of the face’.
2◊◊The extensive relations of the nasal cavity are important in the spread of
infection. Observe that it is in direct continuity with (i) the anterior cranial
fossa (via the cribriform plate of the ethmoid bone); (ii) the nasopharynx
and, through the pharyngotympanic tube, the middle ear; (iii) the
paranasal air sinuses; (iv) the lacrimal apparatus and conjunctiva.
3◊◊The septum is frequently deviated to one or other side, interfering both
with inspiration and with drainage of the nose and accessory sinuses.

The ear

The external ear (Fig. 268)
This comprises the auricle and external auditory meatus. The auricle, for the
most part, consists of a cartilaginous framework to which the skin is closely
applied. The intrinsic and extrinsic muscles described for the ear are of no
significance in man.
The external auditory meatus extends inwards to the tympanic mem-
brane. It is about 1.5in (37mm) long, and has a peculiar S-shaped course,
being directed first medially upwards and forwards, then medially and
backwards and, finally, medially forwards and downwards. The outer
third of the canal is cartilaginous and somewhat wider than the medial
osseous portion. The whole canal is lined by skin, which is closely adherent
to the osseous portion but is separated from the cartilaginous part by the
ceruminous glands in the subcutaneous tissue.
The tympanic membrane, or ear drum (Fig. 268; see Fig. 270), separates the
middle ear from the external auditory meatus. It is made up of an outer