14 PROCEEDINGS OF THE NATIONAL. MUSEUM vol. 67 



of the left glenoid fossa, has been much augmented ,by the rostral 

 twist. In fact the latter is so great that the mandible has resisted 

 it, through the interlocking of the teeth. Thus, the mandibular 

 canines have been forced to incline toward the left, while the max- 

 illary canines and lateral incisors have been pushed toward the 

 right. The result is that although the rostrum as a whole turns 

 strongly to the left, the anterior portion of its alveolar border exhibits 

 a sUghtly dextral counter twist. The mandible reflects the varied 

 stresses in a form difficult to describe with accuracy, but to attempt 

 to do so is hardly necessary. 



Another skull of Euraetoyias jubata showing some asymmetry was 

 also discovered. This is No. 131895 of the United States Biological 

 Survey collection, and bears the data " 9 , California, Santa Cruz Id., 

 W. J. Hockmeier, 4386X." It is of an adult, though not aged 

 individual (pi. 8). The original cause leading to present asymmetry 

 was a pathological condition of the left auditory and petrous tem- 

 poral, which are now misshapen, with rough surfaces, and a large 

 perforation inferiorly. An abscess probably constituted the original 

 cause. The result has been a stunting of the region involved, and 

 the distance from craniad of the glenoid fossa to the paroccipital 

 process is 7 mm. less upon this side than the right. The zygomatic 

 arches are also involved, probably through lack of normal growth of 

 this process of the left squamosal, for the left arch is about 6 mm. 

 shorter than the other. This, in turn, has evidently been instru- 

 mental in limiting the growth of the anterior portion of the tempo- 

 ral muscle, as clearly shown by the differences in the development 

 of the supraorbital processes and the ridging between them. The 

 remainder of the temporal fossae do not show any appreciable 

 disparity, however. 



Very slight asymmetry exhibited by the posterior half of the ros- 

 trum is probably due to dissimilarity in the development of the two 

 zygomatic arches and the temporals, while the decided sinistral twist 

 of the rostral extremity is attributable, through the interlocking of 

 the canines, to the displacement of the left glenoid fossa, and hence, 

 the mandible. 



An interesting point which can hardly be explained entirely by the 

 foregoing conditions is asymmetry in the occipital region. This is 

 precisely the opposite of what might be expected, for the distance 

 between the foraminal margin of the occipital condyle and the paroc- 

 cipital process is, upon the left, 61, and on the right, 54 mm. It is 

 due to growth of the left paroccipital process and the exoccipital 

 rather than to displacement of the foramen magnum. One might 

 hazard the opinion that it is the result of a compensating development 

 of the attached muscles, as the digastric, or to some pathological 



