BONES OF THE HEAD 71 



about 1-J inches from before backward and 1 inch 

 from side to side. Pulsation can be felt over this 

 fontanelle up until the twelfth to twenty-fourth 

 month. It usually disappears by ossification after the 

 second year, but cases have been reported when it 

 persists throughout life. 



The posterior fontanelle is triangular in form and 

 is situated at the junction of the superior angles of the 

 parietal bones with the occipital bone. The lateral 

 fontanelles are irregular in shape, and are located at 

 the antero-inferior and postero-inferior angles of the 

 parietal bones respectively. The posterior and lateral 

 fontanelles close shortly after birth. The lack of 

 ossification in the bones of the skull favors the over- 

 lapping of the bones or moulding of the infant's head 

 during parturition, thus facilitating delivery and pre- 

 venting injury to the mother and child; of course, 

 barring some abnormal condition at the time of birth. 



In adults the skull bones are closely fitted by uneven 

 edges, there being interposed a little fibrous tissue 

 continuous with the periosteum, the dentations are 

 confined to the external table, the edges of the inner 

 table lying in apposition. The lower jaw has a mov- 

 able articulation differing from the others. 



The bones forming the vertex or superior surfaces 

 of the skull are: frontal, two parietal, two temporal 

 (squamous and mastoid portions), and great wing of 

 the sphenoid. 



The Orbital Fossae or Orbits. These are pyramidal 

 in shape, with their bases turned forward and outward. 

 They are just below the supraorbital arches; their 

 inner walls are nearly parallel and the outer walls 

 diverge at slight right angles to each other. Each 

 is formed by seven bones or eleven for the two orbits 

 the frontal, sphenoid, ethmoid, lacrymal, palate, 

 malar, maxilla. The roof of each is formed by the 

 orbital plate of the frontal and small wing of the 

 sphenoid; the floor, by the malar, maxilla, and orbital 



