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, 7.¢. 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; 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 Lehrbuch der Anatomie des Menschen, calls 
special attention to the independent ossification of that which 
becomes the postero-inferior angle of the frontal bone, 2.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.? 
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,” ? 
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. 
? 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 (7.c. 5 to 6 per cent, as compared with but 1 to 2 per cent in 
European skulls). A somewhat similar ‘‘ preinterparietal’’ lying in front of this, 
and which will be described later, occurs in about 1 per cent of all cases. 
