SURFACE OF THE HEAD. 163 



It is bounded anteriorly by the pterygoid fossae and openings 

 of the nose, and behind by the mastoid and condyloid processes. 

 It consists, consequently, in one part, which is horizontal, and in 

 another, which is vertical. In regard to the horizontal portion, 

 its inequalities, processes, and fossae, have been already stated. 

 The relative position of its foramina, cannot, however, be studied 

 except in the united bone. The following rules will afford 

 some assistance in determining their position, even on the liv- 

 ing body. 



A line passing from the anterior margin of one mastoid pro- 

 cess to the corresponding point of the other, will subtend the 

 stylo-mastoid foramina, and the posterior margin of the foramina 

 lac-era; it will also touch the base of the styloid processes, and 

 cut into halves the condyl.es of the occiput. A line, three-eighths 

 of an inch in advance of this, run through the middle of the 

 meatus auditorius externus, will indicate the posterior margins 

 of theglenoid cavities,* and cut in half the inferior end of the ca- 

 rotid orifices or foramina, and touch the anterior margins of the 

 anterior condyloid foramina. Another line, one fourth of an inch 

 in advance of the latter, will cut through the centre of the gle- 

 noid cavity, and subtend the styloid process of the sphenoid 

 bone, and the bony orifice of the Eustachian tube in the tempo- 

 ral bone. A line passing between the external ends of the tuber- 

 cles of the temporal bones, will subtend the foramina ovalia and 

 the foramina lacera anteriora. The foramen spinale is about 

 equi-distant from the last two lines. 



The foramen lacerum anterius, being at the point of the pe- 

 trous bone, is occasioned by the latter not filling up the space 

 between it and the sphenoidal and occipital bones. The de- 

 ficiency is supplied, in the recent state, by cartilage. Precisely 

 opposite to the point of the petrous bone, is the posterior orifice 

 of the foramen pterygoideum, from which emerges the pterygoid 

 nerve, and penetrating this cartilage immediately divides into 

 two branches: one going to the carotid canal, and being one of 

 the roots of the Sympathetic nerve; and the other, ascending 

 into the cranium, becomes the Vidian nerve or superficial pe- 

 trous. 



The vertical portion of the Guttural Region presents the pos- 



* By glenoid cavity is here meant the whole of the depression in the temporal 

 bone, and not merely the surface for the contlyle of the lower jaw. 



