1 32 SKELETON. 



which seems like a part of the glenoid cavity, and is improper- 

 ly considered as such by anatomists, inasmuch as it does not 

 form a portion of the articular surface for the lower jaw, but 

 simply allows room for its motions, the parts which it contains 

 (consisting of vessels, and a portion of the parotid gland) being 

 pressed back when the jaw opens. Between this cavity and 

 the glenoid is the glenoidal fissure, separating the petrous from 

 the squamous bone. In this fissure, leading to the tympanum, 

 is a foramen which contains the processus gracilis of the mal- 

 leus with its muscle, and the chorda tympani. The posterior 

 margin of the depression just alluded to in the petrous bone, is 

 made by a long rough ridge, called processus vaginalis; just 

 behind which, and partially surrounded by it, is the styloid pro- 

 cess. The styloid process is round, tapering, and an inch and 

 a half long ; but frequently absent in prepared skulls, from acci- 

 dental fracture and from being in a cartilaginous state. From 

 it arise the styloid muscles. 



Behind the root of the styloid process, is the stylo mastoid 

 foramen, which transmits the portio dura or facial nerve to the 

 face. Just within the styloid process and the foramen is a deep 

 depression, called jugular fossa, large enough to receive the 

 tip of the little finger. The fossa, along with a corresponding 

 one in the os occipitis, is occupied by the internal jugular vein 

 and the eighth pair of nerves. Immediately before the lower 

 end of this fossa is the foramen caroticum, being the lower ori- 

 fice of a crooked canal, which terminates at the apex of the 

 petrous bone, and transmits the carotid artery and the upper 

 extremity of the sympathetic nerve. At the inner side of the 

 carotid canal, a superficial serrated groove is perceived, which 

 receives the adjoining edge of the occipital bone. Just in ad- 

 vance of the inner part of the jugular fossa is a small spine of 

 bone, at the foot of which is a pit, containing the orifice of the 

 supposed aqueduct of the cochlea. The spine separates the 

 eighth pair of nerves from the internal jugular vein. 



In the angle between the squamous and petrous bones, within 

 the glenoid foramen, is the orifice of the Eustachian tube. The 

 tube is divided longitudinally, by a bony partition. The upper 

 division contains the tensor tympani muscle. 



A small groove exists along the superior angle of the petrous 



