586 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XXXV. — The Inca Bone: Its Homology and Nomenclature. By 
W. Ramsay Smith, D.Sc., M.B., C.M., F.R.S.E., Permanent Head 
of the Department of Public Health of South Australia. 
(MS. received March 18, 1908. Read May 4, 1908.) 
The inca bone in the human skull is usually regarded as the homologue of 
the interparietal of some other mammals. The commonest or best-known 
form of the interparietal occurs in the rabbit as a single somewhat oval 
bone, its long axis being transverse, filling up a space between the parietals 
just in front of the line or curve of the occipital. 
Carl Vogt (. Lectures on Man, London Anthropological Society, 1864) 
makes frequent and detailed reference to a Helvetian skull. From the 
woodcuts, p. 52, fig. 15; p. 66, fig. 22; p. 70, fig. 26; p. 389, fig. 124; and 
p. 390, fig. 125, it is clear that a small round undivided bone occurred in this 
skull in a situation roughly corresponding with the position of the inter- 
parietal in the rabbit. I say “ roughly,” because the posterior border of 
the bone in the Helvetian skull just touches the occipital at the lambdoid 
suture, while in the rabbit the interparietal for about half the extent of its 
perimeter is in contact with the occipital. 
Vogt says (p. 390) regarding the adventitious bone : “ There seems also 
in these Swiss skulls to exist a tendency to the separation of the lambdoid 
suture. The skull from the vicinity of Geneva has that isolated piece of 
bone at the point of this suture, which was formerly considered as peculiar 
to Peruvian skulls, and hence called the bone of the Inca (Os Inca). I saw 
the same thing in some other skulls of Biel and Grenchen, also large 
Wormian bones in the lateral wings of the suture.” 
Deniker (The Races of Man, London, 1900, p. 66) classes the inca bone 
as a Wormian bone, and describes it as being found between the parietal 
bones and the occipital. He gives statistics of its appearance in a perfect 
and an imperfect state in various races. His illustration (op. cit., p. 88) 
represents a large crescentic bone in the position of the membranous portion 
of the occipital. 
Ward (Human Osteology, 3rd edn., p. 34) gives a very complete descrip- 
tion of the occurrence and appearance of Wormian bones, in the course of 
which he describes what is undoubtedly the separate or ununited membran- 
ous portion of the occipital. Bedard’s case, to which he refers, appears to 
