148 



THE SKELETON. 



the carotid canal from the jugular fossa: 6. A small foramen on the inner wall 

 of the jugular fossa, for the entrance of the auricular branch of the pneumogas- 

 tric (Arnold's) nerve : 7. Behind the jugular fossa, 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 pro- 

 cess, 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 

 spina, about an inch in length, continuous with the vaginal process, between 

 the laminae of which it is received ; it is directed downwards, forwards, and 

 inwards, varies in size and shape, and sometimes consists of several pieces 

 united by cartilage; it affords attachment to three muscles, the Stylo-pharyn- 

 geus, Stylo-glossus, and Stylo-hyoideus ; and two ligaments, the stylo-hyoid 

 arid stylo-maxillary: 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 of the petrous portion. 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 the fifth nerve lies. 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 the petrous and squamous portions are seen two 

 canals, separated from one another by a thin plate of bone, the processus coch- 



leariformis; they both lead into the 



Fig. 100. Development of the Temporal Bone, tympanum, the upper one transmit- 

 By four Centres. ting the Tensor Tympani muscle, the 



lower one the Eustachian tube. 



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. 100). The tempo- 

 ral bone is developed by four centres, 

 exclusive of those for the internal ear 

 and theossicula,viz: one for the squa- 

 mous portion including the zygoma, 

 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 

 portion, about the time when osseous 

 matter is deposited in the vertebras ; 

 the auditory process succeeds next ; 

 it consists of a curved piece of bone, 

 forming about three-fourths of a cir- 

 cle, the deficiency being above; it is grooved along its concave surface for 

 the attachment of the meTnbrana tympani, and becomes united by its extremi- 



portions 



I for Stylm'al ptve. 



