18 TPIE TOXEK LECTURES. 



distance from the basioii to the mastoid process, and to the trans- 

 verse process, are also variable without reference to other basic 

 structures. 



In some specimens the differences between the measurements of 

 the anterior cranial segment and those of the occipital bone suggest 

 that the rates of growth in the two parts of the skull have been de- 

 termined by independent causes. 



Thus, when the base of the skull (norma basilaris) is carefully 

 inspected, it is evident that the parts on the sides of a median line 

 are not always of equal value in size ; also that the parts of the ante- 

 rior segment may vary in a manner different from those of the parts 

 posterior to it. In a word, while the contrast of right and left meas- 

 urements are often discernible, the preponderance is not always the 

 same in the two parts. In some examples the left side of the norma 

 is wider throughout, though this is infrequent. In others the left side 

 of the structures posterior to the anterior cranial segment is the wider, 

 while the right side of the anterior segment is best developed. This 

 is a common disposition. In the group last named the increase of the 

 base of the alisphenoid (especially in a backward direction) is associ- 

 ated with a narrowing of the petrosal space — i. e , the space between 

 the alisphenoid and the occipital bones. When this is seen the left side 

 of the dental arch is often more deflected than the right, the right 

 malar bone is the larger and encroaches to a greater degree on the 

 inferior orbital margin, and the surfaces of origin of the right mas- 

 seter and temporal muscles are the better marked. 



The ])roduction of the transverse line intersects the foramen ovale 

 at a point near its posterior margin or at one entirely back of the 

 opening. The left side of the incisive foramen is often the larger, 

 and the suture between the palatal plates of the maxillae is not in 

 line with the basion, but lies to the left. It appears to be probable 

 that the muscles of mastication of the right side are more powerful 

 than are those of the left. Hence the muscular impressions are 

 here most marked and the malar bone is the more robust. The 

 base of the right alisphenoid appears to be forced back, and by 



