THE SKELETON 55 



cranial sutures. In the lower races, as in the Apes, the process 

 always begins anteriorly in the frontal region of the skull, i.e. at 

 the fronto-parietal boundaries, and proceeds backwards. This 

 naturally causes an earlier limitation in growth of the anterior 

 lobes of the brain ; whereas, in the higher (white) races, where 

 the fronto-parietal suture disappears only after the obliteration 

 of the parieto-occipital one, these lobes are capable of further 

 development. This fact may well be closely connected with 

 the intellectual difference between the races. It not infre- 

 quently happens that the frontal suture remains open ; l but 

 whether, as might suggest itself, this is to be regarded as 

 indicative of a further development or, on the other hand, as 

 a reversional feature, cannot yet be decided. On the latter 

 assumption, the fact that fusion of the frontal bones occurs in 

 many Mammals (Apes, Insectivora, Chiroptera, Monotremata, and 

 others) is of interest, especially -as reversion to the condition of 

 the lower Vertebrates is a phenomenon, which, as we have already 

 seen, is by no means unknown in Man. It appears to me that 

 the two views may to a certain extent be harmonised, by con- 

 sidering that the original independence of the ossific centres 

 inherited from lower ancestors may be sometimes retained and 

 utilised in the interest of a progressive development of the 

 anterior lobes of the brain. 



Gegenbaur, in his Lelirbuch der Anatomic des Menschen, calls 

 special attention to the independent ossification of that which 

 becomes the postero-inferior angle of the frontal bone, i.e. that 

 part of it which borders on the alisphenoid. Since, at birth, and 

 even for some time after birth, traces of this division are evident, 

 we are reminded of the post-frontal bone of the lower Vertebrates. 2 



On turning to that part of the skull where the parietals 

 meet the occipital (the lambdoidal suture), an independent mem- 

 brane bone is sometimes found, the so-called " interparietal," 3 



1 According to Welcker, the frontal suture often persists in Caucasians, less 

 often in Malays, and very rarely in Americans, whereas the exact reverse is the case 

 with the transverse occipital suture which divides the interparietal from the occipital 

 bone proper. It often happens that the latter is found together with the frontal 

 suture in one and the same skull. In the child the fusion of the frontal bones begins 

 normally as early as the ninth month, and ends towards the close of the second year. 



2 This must not be confounded with the epipteric bone, which sometimes occupies 

 approximately the same position (cf. infra, pp. 59 and 61). 



3 This is also known as the os transversum, triquetum, epactale, Goetheanum, 

 and most commonly as the os Incae, because of its frequent occurrence in the skulls of 

 the ancient Peruvians (i.e. 5 to 6 per cent, as compared with but 1 to 2 per cent in 

 European skulls). A somewhat similar " prseinterparietal " lying in front of this, 

 and which will be described later, occurs in about 1 per cent of all cases. 



