TEMPORAL BOXE. 



71 



lodges the internal jugular vein, and, with a similar depression on the margin of 

 the occipital bone, forms the foramen lacerum posterius. 5. A small foramen for 

 the passage of Jacobson's nerve (the tympanic branch of the glosso-pharyngeal). 

 This is seen in front of the bony ridge dividing the carotid canal from the jugular 

 iossa. 6. A small foramen seen on the inner wall of the jugular fossa, for the 

 entrance of the auricular branch of the pneumogastric (Arnold's) nerve. 7. Behind 

 the jugular fossa is a smooth square-shaped facet, the jugular surface ; it is covered 

 with cartilage in the recent state, and articulates with the jugular process of the 

 occipital bone. 8. The vaginal process, a very broad sheath-like plate of bone, 

 which extends from the carotid canal to the mastoid process ; it divides behind 

 into two laminae, receiving between them the 9th point for examination, the styloid 

 process ; a long sharp spine, about an inch in length, continuous with the vaginal 

 process, between the laminae of which it is received, and directed downwards, 

 forwards, and inwards. It varies in size and shape ; and sometimes consists of 

 several pieces united by cartilage. It affords attachment to three muscles, the 

 Stylo-phary ngeus, Stylo-glossus, and Stylo-hyoideus ; and two ligaments, the stylo- 

 hyoid, and stylo-rnaxillary. 10. The stylo-mastoid foramen, a rather large orifice, 

 placed between the styloid and mastoid processes ; it is the termination of the 

 aquaeductus Fallopii, and transmits the facial nerve, and stylo-mastoid artery. 

 11. The auricular fissure, situated between the vaginal and mastoid processes, for 

 the exit of the auricular branch of the pneumogastric nerve. 



Borders. The superior, the longest, is grooved for the superior petrosal sinus, 

 and has attached to it the tentorium cerebelli: at its inner extremity is a semilunar 

 notch, upon which reclines the fifth nerve. The posterior border is intermediate 

 in length between the superior and the anterior. Its inner half is marked by a 

 groove, which, when completed by its articulation with the occipital, forms the 

 channel for the inferior petrosal sinus. Its outer half presents a deep excavation, 

 the jugular fossa, which, with a similar notch on the occipital, forms the foramen 

 lacerum posterius. A projecting eminence of bone occasionally stands out from 

 the centre of the notch, and divides the foramen into two parts. The anterior 

 border is divided into two parts, an outer, joined to the squamous portion by a 

 suture, the remains of which are distinct ; an inner, free, articulating with the 

 spinous process of the sphenoid. At the angle of junction of these two parts, are 

 seen two canals, separated from one another by a thin plate of bone, the processus 

 cochleariformis ; they both lead into the tympanum, the upper one transmitting 

 the Tensor tympani muscle, the lower 

 one the Eustachian tube. Fi 



Structure. The squamous portion is 

 like that of the other cranial bones, 

 the mastoid portion cellular, and the 

 petrous portion dense and hard. 



Development (fig. 33). The tempo- 

 ral bone is developed by four centres, 

 exclusive of those for the internal ear 

 and the ossicula, viz.: one for the 

 squamous portion including the zygo- 

 ma, one for the petrous and mastoid 

 parts, one for the styloid, and one for 

 the auditory process (tympanic bone). 

 The first traces of the development of 

 this bone appear in the squamous por- 

 tion, about the time when osseous 

 matter is deposited in the vertebras ; 

 the auditory process succeeds next; 

 it consists of an elliptical portion of 

 bone, forming about three-fourths of 

 a circle, the deficiency being above; it */<" %&^ J 



;. 33. Development of Temporal Bone. 

 By four Centres. 



