188 



THE SKELETON. 



The Fontanelles. 



Before birth the bones at the vertex and side of the skull are separated from each other by 

 membranous intervals in which bone is deficient. These intervals are principally found at the 

 four angles of the parietal bones. Hence there are six fontanelles. Their formation is due to 



FIG. 150. Skull at birth, showing the anterior FIG. 151. The lateral fontanelles. 



and posterior fontanelles. 



the wave of ossification being circular and the bones quadrilateral ; the ossific matter first meets 

 at the margins of the bones, at the points nearest to their centres of ossification, and vacuities 

 or spaces are left at the angles, which are called fontanelles, so named from the pulsations of the 

 brain, which are perceptible at the anterior fontanelle, and were likened to the rising of water 

 in a fountain. The anterior fontanelle is the largest, and corresponds to the junction of the 

 sagittal and coronal sutures; the posterior fontanelle, of smaller size, is situated at the junction 

 of the sagittal and lambdoid sutures ; the remaining ones are situated at the inferior angles of 

 each parietal bone. The latter are closed soon after birth ; the two at the two superior angles 

 remain open longer ; the posterior being closed in a few months after birth ; the anterior remain- 

 ing open until the first or second year. These spaces are gradually filled in 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. 



In addition to the constant centres of ossification of the skull, additional ones are occasion- 

 ally found in the course of the sutures. These form irregular, isolated bones, interposed between 

 the cranial bones, and have been termed Wormian bones or ossa triquetra. They are most 

 frequently found in the course of the lambdoid suture, but occasionally also occupy the situation 

 of the fontanelles, especially the posterior and, more rarely, the anterior. Frequently one is 

 found between the anterior inferior angle of the parietal bone and the greater wing of the 

 sphenoid, the pterion ossicle (Fig. 151). They have a great tendency to be symmetrical on the 

 two sides of the skull, and they vary much in size, 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 Beclard 

 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. 



An arrest in the ossifying process ma} 7 give rise to deficiencies or gaps ; or to fissures, which 

 are of importance in a medico-legal point of view, as they are liable to be mistaken for fractures. 

 The fissures generally extend from the margins toward the centre of the bone, but the gaps 

 may be found in the middle as well as at the edges. In course of time they may become covered 

 with a thin lamina of bone. 



BONES OF THE FACE. 



The Facial Bones are fourteen in number viz. the 

 Two Nasal. Two Palate. 



Two Superior Maxillary. Two Inferior Turbinated. 



Two Lachrymal. Vomer. 



Two Malar. Inferior Maxillary. 



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

 these bones. 



