32 PRACTICAL ANATOMY. 



petrosal nerve to Meckel's ganglion, which is situated in 

 the spheno-rnaxillary fossa. The anterior border of the 

 pterygoid process is broad at the base. Passing down- 

 ward from the Vidian canal is a groove which, in the 

 articulated skull, assists in forming one of the posterior 

 palatine canals. The inner edge of the anterior border is 

 rough, for articulation with the vertical plate of the palate 

 bone. The lower portion of the anterior border is cleft, 

 forming the pterygoid notch, which articulates with the 

 tuberosity of the palate bone. Posteriorly the two plates 

 diverge, the inner being longer, but narrower, than the 

 outer. It terminates in a hook-like process of bone, 

 called the hamular process. The outer plate, broader but 

 shorter than the inner, is directed obliquely backward and 

 outward. Between the plates at the base is a shallow 

 depression, the scaphoid fossa, below which is the ptery- 

 goid fossa, bounded externally by the external plate, 

 internally by the internal plate, and in front by the 

 tuberosity of the palate. The pterygoid plates are 

 mainly for muscular attachment. The sphenoid bone 

 develops by ten centres, which appear from the end of 

 the second month to the middle of the third. At birth 

 it consists of three pieces, which do not join before 

 the end of the first year. 



THE ETHMOID BONE. 



The ethmoid is an irregular bone, and consists of 

 a vertical and a horizontal plate, arranged in the form 

 of a cross, and hanging from the lateral edges of the 

 horizontal plate are the two lateral masses. It is an 

 exceedingly fragile bone about the size of an English 

 walnut. It is placed in the middle line of the skull, and 

 fills the ethmoidal notch of the frontal. It articulates 

 with thirteen bones, the frontal anteriorly, the sphenoid 



