ANATOMY OF THE EAR
nerve through the tympanic plexus and the maxillary division of the trigeminal
nerve through the pharyngeal branch of the pterygopalatine ganglion.
The mastoid bone forms a part of the petromastoid portion of the temporal
bone, the other portions being squamous, tympanic and the styloid process.
It lies below and behind the squamous-and behind and lateral to the petrous
portions. The lower part of the mastoid bone, known as the mastoid process
(Fig. 134), is absent at birth and in the infant the stylomastoid foramen lies
Fig. 133. Vertical coronal section through right
Eustachian tube as seen from the front. 1,
Petrous bone; 2, Cartilage of the tube; 3,
Mucous glands; 4, Levator palati muscle; 5,
Detached and semidetached portions of
cartilage; 6, Fatty and fibrous tissue; 7,
Lumen of the tube; 8, Tensor palati (dilator
Fig. 134. Lateral aspect of left temporal bone. 1, Suprameatal spine; 2, Mastosquamosal suture; 3,
Supramastoid crest; 4, Mastoid foramen (for emissary vein); 5, Fossa mastoidea (surface marking for
tympanic antrum); 6, Mastoid notch for digastric muscle; 7, Site of suture between squama and
mastoid; 8, Tip of mastoid (Note: Dotted lines joining 1, 8 and 3 mark the triangle for operation on
the mastoid); 9, External acoustic meatus; 10, Anterior wail of bony meatus; II, Styloid process; 12,
Vaginal processus of styloid; 13, Petrotympanic fissure (Glaser!an fissure); 14, Mandibular fossa.
(Macewen's triangle—a guide to the position of the antrum—is outlined in white.)