SPHENOID BONE. 



149 



ties to the squamous portion during the last months of intra-uterine life. 

 The petrous and mastoid portions then become ossified, and lastly the styloid 

 process, which remains separate a considerable period, and is occasionally 

 never united to the rest of the bone. At birth, the temporal bone, excluding 

 the styloid process, is formed of three pieces the squamous and zygomatic, 

 the petrous and mastoid, and the auditory. The auditory process joins with 

 the squamous about the time of birth. The petrous and mastoid join with 

 the squamous during the first year, and the styloid process becomes united 

 between the second and third years. The subsequent changes in this bone 

 are, that the auditory process extends outwards, so as to form the meatus audi- 

 torius ; the glenoid fossa becomes deeper ; and the mastoid part, which at an 

 early period of life is quite flat, enlarges from the development of the cellular 

 cavities in its interior. 



Articulations. With five bones occipital, parietal, sphenoid, inferior maxil- 

 lary, and malar. 



Attachment of Muscles. To the squamous portion, the Temporal ; to the zy- 

 goma, the Masseter ; to the mastoid portion, the Occipito-frontalis, Sterno-mas- 

 toid, Splenius Capitis, Trachelo-mastoid, Digastricus, and Eetrahens Aurem; 

 to the styloid process, the Stylo-pharyngeus, Stylo-hyoideus, and Stylo-glos- 

 sus ; and to the petrous portion, the Levator Palati, Tensor Tympani, and Sta- 

 pedius. 



THE SPHENOID BONE. 



The Sphenoid Bone (a^, a wedge] is situated at the anterior part of the base 

 of the skull, articulating with all the other cranial bones, which it binds firmly 

 and solidly together. In its form it somewhat resembles a bat, with its wings 

 extended; and is divided into a central portion or body, two greater and two 

 lesser wings extending outwards on each side of the body ; and two processes, 

 the pterygoid processes, which project from it below. 



The Body is of large size, quadrilateral in form, and hollowed out in its inte- 

 rior so as to form a mere shell of bone. It presents for examination four sur- 

 faces a superior, an inferior, an anterior, and a posterior. 



Fig. 101. Sphenoid Bone. Superior Surface. 



ftnwL dfii Stwi& 



Arttc- 



mm* 



osterior Clincid process 



Joramen Opticu 

 Tora-mtu Lacerum 

 u-s. or Sphi-neiiifalf '* 

 furamf.n JtotanJu 



The superior surface (Fig. 101). In front is seen a prominent spine, the eth- 

 moidal spine, for articulation with the ethmoid ; behind this a smooth surface 



