CONGENITAL FISSURES AND GAPS. 157 



Fig 108. Skull at birth, showing the Anterior Fig. 109. The Lateral Fontanelles. 



and Posterior Fontanelles. 



by an extension of the ossifying process, or by the development of a Wormian bone. Sometimes 

 the anterior fontanelle remains open beyond two years, and is occasionally persistent throughout 

 life. 



SUPERNUMERARY OR WoRMiAN 1 BONES. 



When ossification of any of the tabular bones of the skull proves abortive, the membranous 

 interval which would be left is usually filled in by a supernumerary piece of bone. This is 

 developed from a separate centre, and gradually extends until it fills the vacant space. These 

 supernumerary pieces are called Wormian bones : they are called also, from their usual form, 

 ossa triquetra ; but they present much variation in situation, number, and size. 



They occasionally occupy the situation of the fontanelles. Bertin, Cruveilhier, and Cuvier 

 have each noticed the presence of one in the anterior fontanelle. There are two specimens in 

 the Museum of St. George's Hospital, which present Wormian bones in this situation. In one, 

 the skull of a child, the supernumerary piece is of considerable size, and of a quadrangular form. 



They are occasionally found in the posterior fontanelle, appearing to replace the superior angle 

 of the occipital bone. Not unfrequently, there is one replacing the extremity of the great wing 

 of the sphenoid, or the anterior inferior angle of the parietal bone, in the fontanelle there situated, 



They have been found in the different sutures on the vertex and side of the skull, and in some 

 of those at the base. They are most frequent in the lambdoid suture. Mr. Ward mentions an 

 instance " in which one-half of the lambdoid suture was formed by large Wormian bones disposed 

 in a double row, and jutting deeply into each other ; and refers to similar specimens described 

 by Dumontier and Bourgery. 



A deficiency in the ossification of the flat bones would appear in some cases to be symmetrical 

 on the two sides of the skull ; for it is not uncommon to find these supernumerary bones corre- 

 sponding in form, size, and situation on each side. Thus, in several instances, I have seen a 

 pair of large Wormian bones symmetrically placed in the lambdoid suture ; in another speci- 

 men, a pair in the coronal suture, with a supernumerary bone in the spheno-parietal suture of 

 both sides. 



The size of these supernumerary pieces varies, they being in some cases not larger than a pin's 

 head, and confined to the outer table ; in other cases so large, that one pair of these bones may 

 form the whole of the occipital bone above the superior curved lines, as described by B6clard 

 and Ward. Their number is generally limited to two or three ; but more than a hundred have 

 been found in the skull of an adult hydrocephalic skeleton. In their development, structure, 

 and mode of articulation, they resemble the other cranial bones. 



CONGENITAL FISSURES AND GAPS. 



Dr. Humphry has called attention to "the not unfrequent existence of congenital fissures in 

 the cranial bones, the result of incomplete ossification. These fissures have been noticed in the 

 frontal, parietal, and squamous portion of the temporal bones ; they extend from the margin 

 towards the middle of the bone ; and are of great interest in a medico-legal point of view, as 

 they are liable to be mistaken for fractures. An arrest of the ossifying process may also give 

 rise to the deficiencies or gaps occasionally found in the cranial bones. Such deficiencies are 

 said to occur most frequently when ossification is imperfect, and to be situated near the natural 

 apertures for vessels. Dr. Humphry describes such deficiencies to exist in a calvarium, in the 

 Cambridge Museum, where a gap sufficiently large to admit the end of the finger is seen on 



1 Wormius, a physician in Copenhagen, is said to have given the first detailed description of 

 these bones. 



