A CLINICAL STUDY OF THE SKULL. 67 



NOTES ON SOME OF THE FORAMINA OF THE SKULL. 



The foramina of the skull are chiefly of interest in exhibiting re- 

 tentions of embryonic states. The most striking of these states are 

 seen at the base of the skull, at the region of the union of the vomer 

 with the sphenoid bone and the sjihenoidal processes of the palatal 

 bone and pterygoid process, as ah-eady seen^ (page 23). 



The foramina may be asymmetrical ; the foramen ovale less so 

 than the others. A second grou}) of retention — variations is seen at 

 the surface of the sj^henoid bone, where it lies against the petrosal 

 to form the petroso-sphenoidal suture. Along the lines of this 

 suture are found the oval foramen, the spinous foramen, and the 

 canalis innominata. The suture widens not infrequently at the outer 

 end to form an opening, which may receive the name of the petroso- 

 sphenoidal foramen. The oval, spinous, and petroso-sphenoidal 

 foramina may be confluent, or the spinous and petroso-sphenoidal 

 may alone unite, or the oval and the spinous. The canalis iunomi-- 

 nata^ may be large or absent. In the skull up to the fourth year 

 the spinous and petroso-sphenoidal openings are always united. I 

 have often remarked that the spinous foramen may be entirely 

 absent on one side.^ In some lower animals, as is seen in the Vir- 

 ginian opossum, the foramina retain throughout life the type seen 

 in this disposition to coalescence. 



The development of the tympanic bone is peculiar, for instead of 

 uniformly extending in all its proportions a large foramen is always 

 seen on the bone at its inferior surface. The significance of the 

 opening is unknown. 



The foramen is very variable in form and position. As a rule, 

 it recedes with age from the aperture of the meatus, so that in adult 

 examples the retained foramen is almost always a centimetre or 

 more from the outer free margin. Examples of the retention of the 



^ For a good example see No. 924, negro. 



' The foramina ovale are at times asymmetrical. 



' No. 142, Marquesas (A. N. S.), furnishes an example. 



