OP THE VOMEE, ETHMOID, AND INTEEMAXILLAET BONES. 
293 
possibly about ten or twelve years old. But apparently the most frequent arrangement 
in the adult is that the crista incisiva is prolonged backwards so as to articulate with the 
maxillaries behind the anterior palatine canal ; and in that case, as the maxillary margin 
of the vomer falls short of the canal, the process in question does not exist. 
At an early age the vomer begins to lose its characteristic form and its individuality ; 
and the sphenoidal spongy bones lose theirs even sooner. In consequence of this, the 
ordinary descriptions, however faithfully they may give an account of the appearances 
in adult skulls, are imperfect as descriptions of these separate bones. The fact is that 
the maturity of a skull does not correspond with the period of most perfect development 
of the indi-vidual bones of which it is composed. This is recognized by us when we 
resort to young skulls for specimens of disarticulated bones, and would be acknowledged 
still more readily in describing an elephant’s skull or a whale’s ; but, with regard to 
the bones in question, the period of this most characteristic condition is so early that it 
has escaped due attention, and the natural result has followed, that the adult appear- 
ances have not been properly understood. 
The alterations which the sphenoidal spongy bones undergo take place in connexion 
with the increased hollowing out of the sphenoidal sinuses. As these sinuses dilate, the 
superior plates of the spongy bones are pressed against the body of the presphenoid, 
which also becomes narrowed and deepened, until, instead of a thick bone in the middle 
line and a lamina supporting it on each side, we meet with only one central lamina 
between two large sinuses, and that deviating often a great distance to one side. The 
processes which projected downwards to the vomer disappear by the dilatation of the 
smuses, until there is nothing left of them but a slight ridge corresponding to the edge 
of the vomer ; inside which, what was once a perpendicular lamina forms part of the 
convex floor of the sinus, and on reaching the middle line is incorporated with the body 
of the presphenoid to form the septum sphenoidale. Thus the sphenoidal spongy bones 
become blended wdth the sphenoid, while at the same time their appearance of continuity 
with the vomer is gradually effaced ; so much so, that the latter is habitually and cor- 
rectly described as resting, in the adult, against their under surface. In the Anatomical 
Museum of this University there is a skull, seemingly from a subject about twelve years 
of age, in which the descending processes of the sphenoidal spongy bones have at the 
fore part not yet begun to be rounded away, but articulate accurately edge to edge with 
the vomer. 
The sphenoidal and other sinuses no doubt have the important function of serving as 
caves for the reverberation of the voice, but they are likewise useful in giving lightness 
to the bones they occupy ; and though in old persons they cease to communicate with 
the nose, they nevertheless grow larger and larger as age advances and the bones grow 
denser, until, as in a specimen beside me, the antrum of Highmore invades the malar 
bones, and the sphenoidal sinuses so hollow-out the sphenoid that the walls of the Vidian 
canals are laid bare and traverse them like tubes. In these aged subjects the septum 
sphenoidale is a very thin partition indeed, and is usually very much driven to one side. 
