Department of Anatomy, Dr. V.M. Medical College, Solapur, India
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The squamous occipital bone consists of two parts supraoccipital and interparietal. Usually interparietal bone fuses withsupraoccipital but sometimes remains as separate bone. In this study total 310 adult skulls were examined to determine the incidence of theinterparietal bone. The interparietal bone was observed in 3 skulls (0.99%). Sutural bones (wormian bones named after olasus worm) wereseen in 32 skulls at lambda.
Key words : Interparietal bone, Sutural bones, Wormian bones.
The squamous part of occipital bone consists of supraoccipital and interparietal parts. (Shrivastava, 1977, Arinci and Elhan, 1993). Interparietal part above the highest nuchal line develops in membrane from two pairs of ossification centres. (Shrivastva, 1992). The first pair of centres consists of medial and lateral nuclei and forms two lateral plates and the second pair of centres include upper and lower nuclei and appears between two lateral plates and forms the medial plate. Failure of fusion between these centres of nuclei with each other or with supraoccipital part may give rise to interparietal bone (s). In this study the incidence of interparietal bone in the Western Maharashta region has been estimated and compared with other relevant literature.
A total of 310 adult skulls (200 males & 110 females) were examined to determine the incidence of interparietal bone in Western Maharashtra Region.
Interparietal bone(s) were observed in two male skulls and one female skull (0.99%)
Skull No. 1, Skull No. 2: Both Males.
A single large triangular separate interparietal bone was seen below lambda. This resulted because of failure of fusion between upper and lower nuclei of medial plate (Fig. 1 & Fig. 2). The other ossicles seen in the lambdoid suture were sutural bones. (Wormian bones).
Skull No. 3 : Female
Two large separate interparietal bones seen on left side and right side below lambda are due to failure of fusion of left medial plate with right medial plate and left lateral plate and the other interparietal bone of right side is due to failure of fusion of right medial plate with left medial plate and right lateral plate.
Ranke (1913) described that there were two pairs of ossification centres at interparietal part above highest nuchal line. Sometimes a third pair of centre (Preinterparietal) is seen in addition to two pairs of centres. (Ranke, 1913, Brethnach, 1965, Shrivastava, 1977, Pal, 1984). As per Shrivastava (1977) pre-interparietal bone develops due to presence of the third pair of centres. As per Pal et al (1984) and Pal (1987) the term ‘‘Pre-interparietal’’ is misleading and bones should be referred as upper central piece or pieces of the interparietal bone. According to Shrivastava (1992) pre-interparietal bone develops as a result of failure of fusion between upper and lower nuclei of the medial plate and are actually parts of interparietal bone. He claims that all bones developing in the region of lambda and lambdoid suture outside the limits of interparietal area are sutural or wormian bones with separate ossification centres.
The incidence of interparietal bone (Table-1) was reported as 0.8% by Shrivastava (1977) 1.6% by Singh et al (1979), 2.6% by Pal et al (1984), 4.0% by Cireli et al (1985), 2.5% by Saxena et al (1986), 1.6% by Maden Muftuoglu (1990) and 6.6% by Aycan (1993). In our study the incidence of 0.99% was found.
|Singh et al (1979)||500||1.6|
|Pal et al (1984)||348||2.6|
|Cireli et al (1985)||150||4.0|
|Saxena et al (1986)||40||2.5|
|Magden & Muftuoglu (1990)||420||1.6|
|Katkici & Gumusburum (1995)||302||0.99|
The incidence of preinterparietal bone was 2.9% by Shrivastava (1977); 0.8% by Singh et al (1979), 2.5% by Saxena et al (1986), and 0.8% by Gopinathan (1992). According to Pal et al (1984) a true pre-interparietal bone is triangular in shape and found posterior to lambda. In present study they are found only in two bones (Fig. 1) The bone which was called as pre-interparietal in previous studies is actually part of interparietal or sutural bone. The embryological development of interparietal or sutural part of occipital bone has been clarified with study published by Shrivastva (1992) similar to Pal et al (1984) and Pal (1987). The present study also suggests that the term pre-interparietal is misnomer and should not be used. Our findings in the present study are identical with Kalkici et al (1995).
J. Anat. Soc. India 50(1) 11-12 (2001)
Fig. 1 & Fig. 2 : A single seperate and triangular interparietal bone was seen below lambda as failure of fusion of upper nuclei of medial plate with lower nuclei.
Fig. 3 : Large separate interparietal bone seen on left side and right side below lambda.