i5o8 HUMAN ANATOMY. 



Foreign bodies may lodge in the tube during vomiting, or a broken piece of the 

 bougie may be left in. They will usually escape during vomiting or hawking, or 

 they may be removed by an instrument if visible. 



If the tube is normal, a bougie \]A, mm. in diameter will easily pass the isthmus, 

 the narrowest part. Strictures may be dilated or applications made by bougies. 

 Narrowing of the lumen may occur near the isthmus from chronic inflammation or, 

 at the pharyngeal orifice, from the pressure of pharyngeal adenoids, tumors, or polypi. 



Mastoid Process and Cells. — The mastoid ])rocess which is formed by the 

 posterior extremity of the petrous bone, is relatively small at birth and contains no 

 air cells except the antrum. The antrum is almost constant, although its size varies. 

 In the infant it will hold a small pea, while in the adult its average length is from 12- 

 15 mm. (one-half inch or slightly more), its height 8-10 mm., and its width about 

 7 mm. (Briihl). It is the means of communication between the tympanum and the 

 mastoid cells, so that infection finds an easy passage from the former to the latter. 

 Its distance from the external surface of the mastoid process will depend upon the 

 size of its cavity. This is usually from 12-14 i'''*"''- Anteriorly the antrum opens 

 into the attic portion of the tympanum, and is in almost a direct line through that 

 cavity with the Eustachian tube. A probe passed up the tube from the pharynx 

 would pass through the attic into the antrum and would strike the joint between the 

 incus and the stapes. The axis of the external canal would strike the line at an angle 

 of about thirty degrees. 



The floor of the antrum is belovv^ the level of the entrance into the attic, so that 

 pus in the antrum tends rather to enter the mastoid cells. Sometimes nearly all the 

 mastoid cells are pneumatic ; more frequently they are diploetic at the tip of the 

 mastoid process, and pneumatic above (page 184). Pus in the air spaces may 

 reach the diploetic region by breaking down the thin intervening septa. Those 

 cases in which there are no mastoid spaces are probably sclerotic from pathological 

 causes. Thus a chronic inflammation of the mastoid may give rise to new bone 

 formation, filling the diploe and causing eburnation. This would tend to prevent 

 the outward progress of pus and would favor its extension toward the interior of 

 the cranium. 



The suprameatal spine is about 10-12 mm. above the floor of the antrum, 

 which corresponds to a point about half way up the posterior wall of the bony meatus, 

 and lies about 5 mm. posterior to the inner end. Thus bulging of the posterior wall 

 of the meatus may result from disease in the antrum. The squamo-mastoid suture is 

 frequently seen on the surface of the mastoid process in children, and may give pas- 

 sage to pus from the antrum to the surface. Through deficiencies in the mastoid 

 process near its tip pus may find its way into the sheath of the sterno-cleido-mastoid 

 muscle, or along the large blood-vessels into the neck. 



The bony wall between the antrum and posterior fossa of the skull is thin and 

 cancellous, and may show deficiencies through which pus may reach the posterior 

 fossa. In the fossa on the posterior surface of the mastoid process is the groove 

 for the sigmoid sinus, which is f-requently infected from disease of the antrum. Such 

 infection may extend from the antrum to the posterior or cerebellar fossa of the skull, 

 causing meningitis, septic thrombus of the lateral sinus, or a subdural or cerebellar 

 abscess. 



The possible lines of extension of mastoid inflammation may be summarized as 

 follows (after Taylor) : (i) Up2vard, from absorption of the thin tegmen antri, or 

 through the veins passing up through foramina in the tegmen (causing external 

 pachymeningitis in the floor of the middle cranial fossa), or through the remains of 

 the petro-squamous suture (causing thrombosis of the superior petrosal sinus). (2) 

 Dowmvard, by emissary veins, or through a sinus at the lower part of the mastoid in 

 the digastric fossa (causing cellulitis beneath the sterno-mastoid, or travelling along 

 the stylo-glossus, stylo-pharyngeus and stylo-hyoid to the retro-pharyngeal region). 

 (3) Forzuard, through the thin bony layer separating the external auditory meatus 

 from the antrum and the mastoid cells T causing discharge from the meatus if the 

 perforation is complete, or if it remains subperiosteal, directing the pus outward to 

 a point just back of the pinna). (4) Outward — especially in children — through the 

 thin post-auditory process of the squamous bone, or through the open masto- 



