186 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



tion; synostosis of coronal right and left between steplianion and pterion ; fronto-splienoid sutures 

 coossified riglit and left; very slight commencing lambdoid coossification. This skull is interest- 

 ing, not because the sagittal synostosis is unique, but because it is so complete and apparently so 

 much in advance of the other synostoses, while it retains a globose shape, being notably rounded 

 in its outline. 



No. 1062, a well-preserved skull, with mandible, from Dakota; basilar suture closed; perma- 

 nent teeth all cut and none of them shed ante-mortem; teeth show some wear; sagittal suture 

 obliterated except its anterior two centimeters; no other synostosis. 



Alaskans. — Sagittal synostosis unaccompanied by other synostoses is not conspicuous. Only 

 the following two, the first of which is very remarkable, are worthy of note : 



No. 2J:54r, perfectly preserved, from a child between 7 and 10 years old; basilar suture open; 

 sutures between basi-occipital and exoccipitals partly open; premaxillary suture visible on pala- 

 tine vault; first permanent molars cut and second appearing; upper median, lower median, and 

 lateral incisors cut but lost; no permanent canines or premolars; posterior two-thirds of sagittal 

 suture entirely closed on outer and inner tables; for one-half of the remaiuiug third there is 

 partial synostosis on both tables, while the anterior sixth is open; no other synostosis. 



No. 2486, a perfectly preserved skull of an adult; basilar suture not quite closed; lower third 

 molars not cut; posterior two-thirds of sagittal firmly coossified; half the remainder partially so; 

 anterior extremity open ; coossification also, but less complete, of right coronal between sagittal 

 and temporal line, right lambdoid and left j)arieto-mastoid. 



Eskimos. — Among the Greenland Eskimos there is no case of sagittal synostosis, alone, com- 

 parable with that of the Arizouiaus. There is found, however, the following extraordinary 

 specimen : • 



No. 1220, a skull without mandible, of light weight and well preserved; basilar suture open; 

 teeth lost post mortem, except the I'ight upjier molars, three in number, and left upper first molar; 

 both third molars cut. The one remaining in the skull is not worn, nor is the second molar much 

 worn ; dentine of first molar worn a little; complete sagittal obliteration; also complete lambdoid 

 obliteratiim except about 5"""' of the left lateral end; no other synostosis. Thus the whole pos- 

 terior end of the skull from the coronal suture above to the basilar suture below is a single bone. 



We conclude then: First, that unique sagittal synostosis may take place at a very early age; 

 second, that it does not necessarily produce a scaphoid skull; third, that it may or may not be 

 accompanied by a sagittal ridge; fourth, that at present it can not be said to be peculiarly charac- 

 teristic of any American race. 



Percentages representing the number of cases of unique sagittal synostosis in relation to the 

 total number of skulls in each given series might be reckoned; but they would probably not 

 accurately rei>reseut the teudency to unique sagittal synostosis for the following reasons: 



First. It is most likely true that under a certain age no skidl is liable to sagittal synostosis 

 except for pathological reasons. Diseased skulls should of course be excluded from consideration 

 and not be allowed to affect the percentage. But, inasmuch as we have learned that sagittal synos- 

 tosis may take place before the skull is matured in any .other respect, we must confess ourselves 

 at a loss to determine exactly what that age is. So then we uuxst either draw au arbitrary line 

 between two supposed classes of skulls, the one of which is liable and the other not liable to 

 sagittal synostosis, or we must consider every skull as liable to it. In neither case can our per 

 ceiitage exactly represent the facts. 



Second. Cases of sagittal obliteration may occur which are striking in their completeness, but 

 which are accompanied by very slight disseminated synostosis of other sutures. In determining 

 whether such cases are to be allowed to affect the percentage or not, personal judgment — always a 

 little arbitrary — must be used. 



Third. Cases may occur Avhere the sagittal is coossified but not entirely obliterated, while all 

 other sutures are completely open. This occurrence in a young skull merits mention; but here 

 again fallible judgment is called into play to pass upon the age of the skull and the minimum 

 amount of synostosis entitled to mention. 



