The nature of the Fontanelles (soft spots) and the Sutures (line/cracks).

At birth, the skull of a newborn consists of many bones. The top of the skull consists of 7 big bones. See Picture 1: two frontal bones marked with a red color, two parietal side bones marked with a green color, two temporal bones marked with a dark green color, and one occipital back bone marked with a purple color. These 7 bones are separated by narrow gaps that are seen as lines or cracks, and each of them is filled with a connective tissue. These lines/cracks are known as the cranial sutures. 

There are 6 wide gaps between the bones of the skull of an infant. These gaps are known as fontanelles, and each of them is filled with a membranous connective tissue (see Picture 1, the gaps are marked with grey numbers). Fontanelles are often referred to as soft spot and they are one of the most prominent anatomical features in the skull of a newborn baby. The six fontanelles are present during infancy, with the most notable one, being the anterior fontanelle (picture 1, number 2 in the front) and the posterior fontanelle (Picture 1 number 5 in the back). The morphology of the fontanelles may vary between infants, but characteristically, they are flat and firm. The average closure time of the anterior fontanelle ranges from 13 to 24 months [133]. The connective tissue of the sutures, and the membranous connective tissue of the fontanelles are made from fibers, cells and a gelatinous material [132], not even air can pass through them.

​

Picture 1: The parts of the skull of a baby as viewed from the top of the skull (modified from [p3])

​

​

​

​

​

 

 

 

 

 

 

 

​

​

​

​

​

​

​

​

 

 

 

 

 

 

The functions of the fontanelles (soft spots) and the sutures (lines/cracks).

The fontanelles and the sutures in the skull of a baby play two major functions.

1. At birth, the spaces of the fontanelles (soft spots) permit the movement of the cranial bones and their overlapping at the sutures (lines/cracks) under the pressure of the childbirth. This process reduces the diameter of the skull of a baby and enables it to pass through the narrow birth canal (Picture 2) which is encircled by the pelvis bones (Picture 3) [126].

2. After birth, the fontanelles and the sutures enable the skull to expand with the rapidly growing brain. The fontanelles are the first to close and they will be fused around 18 to 24 months after birth. The sutures, even though are not visible, get closed gradually. The last of the sutures will be closed and fused when the child is an adult and he or she is around 24 years old, while [127].

​

1. Fontanelles and sutures enable the head of a baby to pass through the narrow birth canal which is encircled by the pelvis bones.

During the delivery there is a great pressure on the head of a baby. There are two obstacles: one is the narrow cervix and the vagina (Picture 2) and the second is the pelvis bones (Picture 3). The womb lies on the pelvis bones (the womb is represented by the red elliptic shape in Picture 3). The cervix which is followed by the narrow vagina (Picture 2) descends through the pelvis bones ring (see red arrow in Picture 3). Even thought the cervix and the vagina are elastic and can expand, the pelvis bones 

which form a hard circle around the vagina, limit the extend in which the vagina can expands. 

        

Picture 2: The pregnant womb=uterus [p4],

Picture 3: The pelvic brim bones, and the position of the baby when he or she is about to pass in the birth canal that passes through the pelvis bones [p5]

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As a result of the pressure on the bone plates of the skull of a baby, the bones are shifted, and they are slightly overlaps each other at the sutures. Immediately after birth we can feel along the head protruding lines (where the sutures are). These are the places where the bone plates of the skull overlap each other. The fontanelles which are the big gaps allow bigger bending of the skull (Picture 4 A1). If there were no empty spaces between the cranial bones, which means that the cranial bones were joined together to form one solid piece, the skull might have cracked under the pressure of the delivery. However, the connective tissues that fills the sutures and the fontanelles function as seams, and they are highly necessary to facilitate the movement of the cranial bones forward and backward. Forward, to enable the over lapping of the bones when the head of the baby passes through the cervix and the narrow birth canal-vagina (Picture 2) between the pelvis bones (Picture 3).  Backward, immediately after birth, to enable the cranial bones to shift gradually to their original places as it was in the womb, so the lines of the sutures can not be seen again. This is how the skull endures the high pressure that is applied on it during the delivery without causing damage to the brain.  

​

Picture 4 on the left shows the cranial bones (A) and the brain (B) of a baby in the womb. Picture 4 on the right shows the cranial bones (A1) and the brain (B1) of a baby during delivery while passing in the vagina. The shifting of the cranial bones between pre-delivery in the womb and during delivery in the vagina changes temporally but drastically the shape of the brain as seen in picture 4 B1 on the right. Immediately after the head of the baby emerges out, the shape of the brain returns to the normal shape as it was in the womb (Picture 4A on the left) [140].

​

Picture 4: Three-dimensional magnetic resonance imaging of the molding of the head of a fetus and the changing of the shape of the brain during the labor (modified picture from [140]).

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

 

​

However, not always the returning of the cranial bones to their original position is fully achieved immediately after birth. Then, the protruding suture can be seen and felt. There is no need to intervene in this process, the head will gain its original position naturally few days or weeks after the birth. With out the existence of the sutures and the fontanelles in the skull of a baby, such changes could not have happened to enable the safety passage of the baby through the cervix, the vagina, and the pelvis.

​

2. The fontanelles (soft spots) and the sutures (lines/cracks) enable the head of a baby to continue growing rapidly during infancy.

The baby grows in size and gains weight every day. What about his or her brain? It also grows in size! The fontanelles and the sutures enable the skull to expand too with the rapidly growing brain by allowing the bones of the skull to continue growing along the space of the fontanelles and the sutures. When the baby is born the nurse measures the circumference of his or her head (Picture 5). The normal size is between 30.3 and 37.4 centimeters for girls and 30.7 and 38.3 centimeters for boys. The nurse will continue to measure the circumference of the head of the newborn baby during the first year of the life of the baby. A measurement that is out of the normal range (Picture 6) may show on a problem in the normal development of the skull of a baby. If the skull is too small, it may show on an earlier fusion of the cranial bones and the result of this would be that the brain of the baby will not develop to its full size. If the head of a baby is too big it can show on an accumulation of excess liquid around the brain. This would result in putting pressure on the brain and destroys some of its nerve cells. Regulating the size of the head of a baby is therefore very important to prevent an abnormal development and a low cognitive function of the baby. Picture 6 shows how fast the head of a baby grows. If the skull of the baby was one whole bone it would not enable the expansion of the head. Therefore, nature creates the skull of the baby not as one big bone but as several pieces (plates) of bones that even though they are separated from each other, they are connected one to another with a flexible special material called connective tissue. Each of these bones grows and expands gradually until after many months the big spaces (soft spots or fontanelles) between them are closed and some of the narrow spaces (lines or sutures) are closed only years after birth. It is because the brain grows for many years and puberty age is not only when the body matures but also when the brain is almost fully mature. The brain which controls everything in the body takes even a longer time to be mature than the other organs in the body. It is the most complicated and delicate organ in the body. If any of the suture (lines/cracks) will be closed before the time, the bones that boarder that suture will not be able to grow and expand in that direction. As a result of that the skull will have an abnormal shape. 

 

 

                     Picture 5: How to measure the circumference of the head of a baby [p6].

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

​

 

Picture 6: The ratio of the growth of the head of a baby boy during the period of one and half year of his life (based on World Health Organization, Child growth standard, (median measurement) [141]).

The circumference of the head of a baby girl is a little bit smaller than that of the head of a boy.

 

 

 

​

​

​

​