72 



THE SKELETON. 



as follows : the part of the squamous temporal which supports it lies at first below 

 the level of the zygoma. As, however, the base of the. skull increases in width, 

 this lower part of the squama is directed horizontally inward to contribute to 

 the middle fossa of the skull, and its surfaces therefore come to look upward and 

 downward. The mastoid portion is at first quite flat, and the stylo-mastoid fora- 

 men and rudimentary styloid process lie immediately behind the entrance to the 

 auditory meatus. With the development of the air-cells the outer part of the 

 mastoid portion grows downward and forward to form the mastoid process, and 

 the styloid process and stylo-mastoid foramen now come to lie on the under 

 surface. The descent of the foramen is necessarily accompanied by a correspond- 

 ing lengthening of the aqueduct of Fallopius. 



The downward and forward growth of the mastoid process also pushes for- 

 ward the tympanic plate, so that the portion of it which formed the original floor 

 of the meatus and containing the foramen of Huschke is ultimately found in the 

 anterior wall. With the gradual increase in size of the petrous portion the 

 floccular fossa or tunnel under the superior semicircular canal becomes filled up 

 and almost obliterated. 



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 (<r^v, 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. 



Middle clinoid process. 

 ^Posterior clinoid process 



Ethmoidal 

 spine. 



Foramen opticum. 

 Foramen lacerum ante- 

 rius or Sphenoidal 

 fissure. 



Foramen rotundum. 



Foramen Vesalii: 



Foramen ovale. 



Foramen spinosum. 



FIG. 37. Sphenoid bone. Superior surface. 



The body is of large size, 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. 37). In front is seen a prominent spine, the 



