ART. 27 ASYMMETRY IN SKULLS OF MAMMALS — HOWELL 9 



are otherwise of equal development, it is impossible now to be sure 

 whether the muscles passing beneath (withili) the arch were of greater 

 bulk upon one side than the other, or whether the masseter of one 

 differed somewhat in development from its fellow^. 



The right coronoid process is about 5 mm. longer than the left, but 

 this is due to the fact that the mandibular notch is correspondingly 

 lower upon that side, and not to diffeiences in the lower-border-to- 

 coronoid measurement. The reasons for this state of affairs are too 

 obscure and complicated for satisfactory interpretation. 



At first thought it would appear that the displacement towards 

 the right of the rostrum is attributable to the effect of the teeth of 

 the mandible having been pulled in that direction by the action of 

 the asymmetrical muscles attached to the latter. Although it seems 

 that this hypothesis should be the logical one, a closer scrutiny of 

 the existing state of affairs demonstrates that the rostrum {i. e., the 

 portion of the face craniad to the frontals and orbits) primarily has 

 been deflected towards the right. The reason for this rostral move- 

 ment is' obscure. As there are no powerful muscles connected with 

 this region, it can only be presumed that the displacement was in 

 response to certain muscular forces operating asymmetrically upon the 

 bones with which the rostrum articulates. It is clear that the man- 

 dible, through its condylar articulation, has resisted this dextral trend 

 of the rostrum. The lower border of the mandible exhibits a tendency 

 to remain in normal position, while the alveolar margin, in response 

 to the force exerted by the teeth of the rostrum with its dextral 

 twist, is also twisted towards the right. 



Extremely grotesque is the skull of a monkey (pis. 1 and 2) — Lasi- 

 opijga griseoviridis (Desmarest) — for the loan of which I am indebted, 

 through Dr. G. M. Allen, to the Museum of Comparative Zoology. 

 This is a fully adult male (No. 15720, Mus. Comp. Zool.), bearing 

 the data "Sudan, Blue Nile, Magangani, 29 Jan., 1913, Philhps 

 Sudan Ex. 1913, Col. G. M. Allen, J. C. Phillips, orig. 84". Recent 

 injuries, received by the skull at the time when the specimen was col- 

 lected, consist of the breaking away of a part of the upper alveolar 

 border, including the two left incisors, and injury to the right tem- 

 poral, including mastoid, auditory and squamous portions. Old 

 osseous scars comprise a fracture of the nasal bridge, which probably 

 has had no effect upon the conformation of the skull, the absence of 

 the right lateral, maxillary incisor, broken off at the root, and the 

 absence of the entire posterior portion of the left ramus of the man- 

 dible, including angular process, the whole condyle, and all but the 

 extreme anterior border of the coronoid process. There is no indi- 

 cation of disease, so it is likely that the mandibular fracture was due 

 to an accident of some sort, such as a glancing rifle ball or a long fall. 

 The portions of bones detached were either absorbed, or sloughed off 

 53194—251 2 



