180 SKELETON. 



the fontanels. They ossify rapidly after birth, and are fre- 

 quently closed completely by the end of the first year ; but if 

 there be an accumulation of water in the ventricles of the brain, 

 they remain open for an indefinite period. 



The longest diameter of a child's head is from the vertex or 

 posterior extremity of the sagittal suture to the chin, and mea- 

 sures five inches and a quarter. From the middle of the frontal 

 bone to the tubercle of the occipital is four inches, from one 

 parietal protuberance to the other is about three inches and a 

 half. 



At birth the os frontis consists, most commonly, of two pieces, 

 united by the sagittal suture. The parietal bone is a single 

 piece, incomplete at its angles. The temporal bone consists of 

 three pieces: one is the squamous, the other is the petrous, and 

 the third is a small ring which afterwards constitutes the meatus 

 externus; it is deficient in styloid and mastoid processes. The 

 os occipitis is in four pieces: one extends from the angle of the 

 lambdoidal suture to the upper edge of the foramen magnum; 

 on either side of the foramen magnum is another, with the con- 

 dyle growing on it, and the cuneiform process is the fourth. The 

 ethmoid bone is cartilaginous. The sphenoidal bone is in three 

 pieces. The body and little wings, being united, form one ; the 

 great wing and the pterygoid process, being also united, form 

 on either side of the body another piece. 



At birth there is a great disproportion in size between the cra- 

 nium and face. This disproportion diminishes in the progress 

 of life, by the development of the sinuses and of the alveolar 

 processes in the latter. At birth, indeed, there is no cavity ei- 

 ther in the sphenoidal, the frontal, or the upper maxillary bones; 

 the orbitar and the palate plates are very near each other, and 

 the rudiments of the teeth are hidden in the bodies of the up- 

 per and lower jaw bone. The latter consists of two pieces, 

 united by cartilage at the chin, and its angle is very obtuse. 



