64 TEMPORAL BONE. 



through life. The frontal sinuses make their appearance during the fin>t 

 year, and increase in size until old age. 



Articulations. With twelve bones : the two parietal, the sphenoid, 

 ethmoid, two nasal, two superior maxillary, two lachrymal, and two 

 in alar. 



Attachment of Muscles. To two pairs: corrugator supercilii, and tem- 

 poral. 



TEMPORAL BONE. The temporal bone is situated at the side and base 



of the skull, and is divisible into a squamous, mastoid, and petrous portion. 



The Squamous portion, forming the anterior part of the bone, is thin, 



translucent, and contains no diploe. Upon its external surface it is 



smooth, to give attachment to the fleshy fibres of the temporal muscle, 



and has projecting from it an arched 

 g * 28> and lengthened process, the zygoma. 



Near the commencement of the zygo- 

 ma, upon its lower border, is a projec- 

 tion called the tubercle, to which is at- 

 tached the external lateral ligament of 

 the lower jaw, and continued horizon- 

 tally inwards from the tubercle, a 

 rounded eminence, the eminentia arti- 

 culnris. The process of bone which 

 is continued from the tubercle of the 

 zygoma into the eminentia articularis 

 is the inferior root of the zygoma. The 

 superior root is continued upwards 

 from the upper border of the zygoma, 

 and forms the posterior part of the temporal ridge, serving by its projec- 

 tion to mark the division of the squamous from the mastoid portion of the 

 bone ; and the middle root is continued directly backwards, and termi- 

 nates abruptly at a narrow fissure, the fissura Glaseri. The internal sur* 

 face of the squamous portion is marked by several shallow fossae, which 

 correspond with the convolutions of the cerebrum, and by a furrow for 



or coronal border of the bone ; the figure is situated near that part which is bevelled at 

 the expense of the internal table. 4. The inferior border of the bone. 5. The orbital 

 plate of the left side. 6. The cellular border of the ethmoidal fissure. The foramen 

 caecum (2) is seen through the ethmoidal fissure. 7. The anterior and posterior eth- 

 moidal foramina ; the anterior is seen leading into its canal. 8. The nasal spine. 9. The 

 depression within the external angular process (12) for the lachrymal gland. 10. The 

 depression for the pulley of the superior oblique muscle of the eye ; immediately to 

 the left of this number is the supra-orbital notch, and to its right the internal angular 

 process. 11. The opening leading into the frontal sinuses: the leading line crosses the 

 internal angular process. 12. The external angular process. The corresponding parts 

 are ?een on the other side of the figure. 



* The external surface of the temporal bone of the left side. 1. The squamous por- 

 tion. 2. The mastoid portion. 3. The extremity of the petrous portion. 4. The zy- 

 goma. 5. Indicates the tubercle of the zygoma, and at the same time its anterior root 

 turning inwards to form the eminentia articularis. 6. The superior root of the zygoma, 

 forming the posterior part of the temporal ridge. 7. The middle root of the zygoma, 

 terminating abruptly at the glenoid fissure. 8. The mastoid foramen. 9. The meatus 

 auditorius externus, surrounded by the processus auditorius. 10. The digastric fossa, 

 situated immediately to the inner side of (2) the mastoid process. 11. The stylpid 

 process. 12. The vaginal process. 13. The glenoid or Glaserian fissure ; the leading 

 line from this number crosses the rough posterior portion of the glenoid fossa. 14. The 

 '*oening and part of the groove for the Eustachian tube. 



