THE CRANIUM. 171 



the sphenoid (Fig. 137); it remains in this condition in all 

 mammals except man. In him the margins of the bone on each 

 side grow out and fuse and thus convert the notch into a foramen. 

 Other examples are the foramen spinosum, the foramen rotundum, 

 parietal foramen, mastoid, etc. 



Wormian Bones. — In the six fontanelles which occur at the 

 parietal angles separate ossific centres frequently appear and close 

 them. The fontanelle ossifications form "Wormian bones. They 

 occur most frequently at the posterior angles of the parietal 

 (Lambda and Asterion) but they are also common at the Pterion 

 (epipteric Wormian) and rare at the Bregma. The wormian at 

 the last-mentioned point receives the name of os anti-epilepticum. 

 Much confusion has been caused by naming a large wormian, 

 which may occur in the lambdoidal (posterior-superior) fontanelle, 

 the inter-parietal bone. 



The Inter-parietal Bone. — It has already been shown that 

 the part of the supra-occipital above the superior curved lines is 

 developed from membrane by two centres of ossification and is at 

 first and almost until birth nearly separated from the lower part 

 developed from cartilage (Pig. 132). The membranous part of the 

 supra-occipital represents the inter-parietal bone. In marsupials, 

 ruminants, and ungulates, the inter - parietals fuse with the 

 parietals and not with the occipital. In rodents they fuse 

 with both occipitals and parietals. In primates and carnivora, 

 as in man, they fuse with the occipital. It is extremely rare 

 to find the whole inter-parietal separate in man, but a large 

 wormian, partly replacing the inter-parietal, is very frequent. 

 Such a wormian bone, if large, is named variously, os epactal, 

 os Incae, os triquetrum, or pre-interparietal. 



The Post-frontal does not occur in mammals as a separate 

 bone ; in them it has fused with the frontal, and forms that part 

 of the bone which articulates with the great wing of the sphenoid 

 and malar. A wormian bone — the epipteric — which is occasion- 

 ally developed in the fontanelle at the pterion, may be mistaken for 

 it. Traces of a true post-frontal, partly separated from the frontal, 

 rarely occur in man. The suture round a wormian bone may be 

 mistaken for a fissure or fracture when exposed by the trephine. 



The Cephalic Index. — Anthropologists have employed the 

 shape of the head as a character in classifying the races of man- 



