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No. 8.— On certain Vacwities or Deficiencies in the Crania of 
Mammals. By D. D. SLADE. 
CERTAIN vacuities or deficiencies, ranging much in size, position, and 
relation to neighboring parts, exist in the macerated adult skull of the 
various orders of the Mammalia. 
These vacuities are in themselves due to an arrest of osseous develop- 
ment, and are in no wise to be confounded with the air cells in the can- 
cellous tissue, such as exist for example in the skull of the Elephant, 
or between the frontal plates of the Ox. These are secondary to the 
original growth of the bone. 
Neither are they, in any sense, the product of absorption. 
They occur for the most part at the juncture, or at what, under other 
circumstances, would be the juncture, of two or more bones, the margins 
of these bones thus becoming the boundary of the vacuity. They 
may also occupy the central portions of a bone, or they may hold the 
position of an ordinary foramen, or of two or more of these combined, 
thus representing, and even becoming in a true signification, enlarged 
foramina. 
The vacuities may therefore be arranged under two categories :— 
1. Those that are dependent upon arrested ossification, in the body 
of a bone, or at a point where several bones would otherwise come in 
contact, but neither of which has any special adaptation to function. 
2. Those that are due to enlarged openings, the result of arrested 
ossification, which have adaptation to special function, and retain this, 
notwithstanding the modifications which they may have undergone. 
The regions of the skull occupied by these vacuities may be thus 
classified : 1. Basal (posterior and lateral) ; 2. Orbito-nasal; 3. Pala- 
tine; 4. Facial; 5. Occipito-squamosal; 6. Squamosal. 
1. Under the term “ Basal” are included the posterior, lateral, and 
postero-lateral regions of the base of the skull, comprehending under 
this last that space existing between the posterior and middle cranial 
segments which in many cases is imperfectly filled by the periotic, 
tympanic, and squamosal, whereby deficiencies differing much in size 
are produced. 
VOL. XIII. — NO. 8. 16 
