72 OSTEOLOGY. 



is grooved along its concave surface for the attachment of the membrana tympani, 

 and becomes united by its extremities 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 at about the ninth month. 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 the extension outwards of the auditory process, so as to form the meatus 

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

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

 cellular cavities in its interior. 



Articulations. With five bones, occipital, parietal, sphenoid, inferior maxillary 

 and malar. 



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

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

 Splenius capitis, Trachelo-mastoid, Digastricus and Eetrahens aurem; to the 

 styloid process, the Stylo-pharyngeus, Stylo-hyoideus and Stylo-glossus ; and to 

 the petrous portion, the Levator palati, Tensor tympani, and Stapedius. 



THE SPHENOID BONE. 



The Sphenoid bone (otyv, a wedge; f?Soj. likeness) 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 interior 

 so as to form a mere shell of bone. It presents for examination four surfaces 

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



The superior surface (fig. 3-i). From before, backwards, is seen a prominent 

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



Fig. 34. Sphenoid Bone. Superior Surface. 



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