434 CRANIA FROM THE MOUNDS OF FLORIDA. 



varied experiences which the specimens have undergone. The protection of all 

 surfaces by embalmment is widely contrasted with those which had been exposed to 

 the air. In the one case the bones are of normal texture though brittle, in the other 

 this has been modified by the disintegrating effect of frost, heat, moisture, etc. 

 Texture and color are often of value in identification. Skulls that are smoke-stained 

 have been shelved or hung over open fires ; those that are calcined have been acted 

 upon by intense heat; those that are at one place earth-stained and at another 

 bleached, marked with confervas or lichens, show scant burial ; those having the eth- 

 moid cells mutilated by insects and filled with pupa cases have been laid on plat- 

 forms or in trees, some show grooves from the teeth of rodents, the details often 

 denoting the species that have committed the ravages. The white appearance of 

 other specimens accompanied with a pitted effect on the surfaces demonstrates the 

 action of a tropical sun and of high winds long driving sand against the bones. 



(15). The functions determining the form of the skull. Among the mechani- 

 cal factors which modify the shape of the skull are the following : 



The growth of the brain. 



The interstitial changes in the bones themselves leading to inflations, which 

 may receive the name of the ethmo-maxillary, the fronto-maxillary, the mastoid, 

 the petrosal and ex-occipital inflations, respectively. 



The action of the muscles attached to the skull. 



Of the first and second of these subjects the general fact is alone appreciated, 

 but the differences within the normal range of variation are imperfectly, if at all 

 known. What are the forces which determine the variations in the shape of the 

 frontal and occipital bones ? Why are some skulls widest at the bi-tuberal and 

 others at the bi-squamosal diameter ? Why do some skulls exhibit the union of 

 the parietal with the alisphenoid bones, while others the union of the squamosal 

 with the frontal ? In like manner one may ask what are the causes of variation 

 in the size of the sinuses ? As a rule the sinuses are most developed in short faced 

 and least developed in the long faced skulls, but the connection between these states 

 is obscure. I refer in this connection to a communication by myself in the Proceed- 

 ings of the Academy of Natural Sciences of Philadelphia, 1894, p. 181. Evidence 

 was educed from the Mammalia in support of the proposition that among the changes 

 that take place in the skull incident to shortening of the face axis the formation 

 of 1 sinuses and pneumatic areas hold an important place. 



It is far different, however, with the muscular forces which are exerted on the 

 periphery of the skull. These doubtless correlate with the prominence of muscular 

 ridges and the depth of fossae While the general statement is true that shapes of 

 bones are due in a measure to the muscles which are attached to them, it remains 

 also true that, in craniology at least, we are needing precision of statement regard- 

 ing the exact influence exerted by the muscles upon the shape of the several bones. 

 Eight of the fourteen cranial bones (viz. : — the frontal, malar, inferior maxillary, 

 palatal, parietal, temporal, sphenoid and occipital bones) yield origin or insertion to 

 muscles, and, without exception, the shapes of all these bones are so modified. 



