180 



THE SKELETON. 



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 fifteen : 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 Retrahens aurem ; 

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

 and to the petrous portion, the Levator palati, Tensor tympani, Tensor palati, and 

 Stapedius. 



The Sphenoid Bone. 



The Sphenoid Bone (a</>qv, 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 outward on each side of the body, and two processes the pterygoid 

 processes which project from it below. 



The body is of large size, cuboid 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. 143). In front is seen a prominent spine, the 

 ethmoidal spine, for articulation with the cribriform plate of the ethmoid ; behind 



Middle dinoid process 

 Posterior dinoid process. 



Ethmoidal 

 spine. 



Foramen opticum 

 Foramen lacerum ante 

 rius or Sphenoidal 

 fissure. 



Foramen rotundum. 



Foramen Vesalii: 



Foramen ovale. 



Foramen spinosum. 



cs 



FIG. 143. Sphenoid bone. Superior surface 



this a smooth surface presenting, in the median line, a slight longitudinal eminence, 

 with a depression on each side for lodging the olfactory tracts. This surface is 

 bounded behind by a ridge, which forms the anterior border of a narrow, trans- 

 verse groove, the optic groove ; it lodges the optic commissure, and terminates on 

 either side in the optic foramen, for the passage of the optic nerve and oph- 

 thalmic artery. Behind the optic groove is a small eminence, olive-like in shape, 

 the olivary process ; and still more posteriorly, a deep depression, the pituitary 

 fossa, or sella turcica, which lodges the pituitary body. This fossa is perforated 

 by numerous foramina, for the transmission of nutrient vessels into the substance 

 of the bone. It is bounded in front by two small eminences, one on either side, 

 called the middle dinoid processes (xXivq* a bed), which are sometimes connected 

 by a spiculum of bone to the anterior clinoid processes, and behind by a square- 



