THE BONES OF THE HEAD ISS 



The posterior fossa is grooved by the following venous sinuses : 

 the lateral sinus, which extends from the internal occipital pro- 

 tubercince to the jugular foFcimen, grooving in its sinuous course 

 the tabular part of the occipital, the postero-inferior angle of 

 the parietal, the mastoid portion of the temporal, and the jugular 

 process of the occipital, (opening from which there is usually 

 the mastoid foramen, and occasionally the posterior condylar 

 foramen) ; the superior petrosal sinus, which grooves the superior 

 border of the petrous bone ; the inferior petrosal sinus, along the 

 course of the petro-basilar suture ; and the occipital sinus, which 

 sometimes grooves the internal occipital crest. 



Wormian Bones. 



The Wormian bones (so named after Wormius) are supernumerary 

 bones which are frequently met with in the course of the cranial 

 sutures, and occasionally in the face, as in the region of the laclu-5anal 

 bones, and at the outer extremity of each spheno- maxillary fissure. 

 From their position in the course of sutures they are known as 

 ossa suturarum. They are for the most part of small size and 

 triangular outhne, and are hence sometimes spoken of as ossa 

 triqueira. They are usually due to the appearance of special 

 ossific centres. Their most common situation is along the course 

 of the lambdoid suture, where they may form a regular chain. 

 The superior angle of the occipital sometimes persists as a Wormian 

 bone, called pre-interparietal, which may be double. One is often 

 found between the an tero- inferior angle of the parietal and great 

 wong of the sphenoid in the region of the pterion, and it is known 

 as the epipteric bone. If the me topic or frontal suture is persistent 

 one or more Wormian bones may be present along its course, and, 

 if at the upper part, they may give rise by their persistence and 

 union to a bregmatic bone. In the condition known as chronic 

 hydrocephalus Wormian bones of large size are present in great 

 numbers along the cranial sutures. 



The SkuU at Birth. 



The skull at birth is remarkable for its large size, and for the 

 great development of the cranimn as compared with the face. The 

 face is equal to one-eighth of the cranium, whereas in the adult 

 it is equal to one-half. The occipital, parietal, and frontal regions 

 are well developed, the parietal and frontal eminences are very 

 conspicuous, and the mastoid processes are absent. The bones 

 are not united by sutures, but are connected by fibrous tissue, 

 continuous with the periosteum externally and diua mater inter- 

 nally. Membranous intervals exist between the angles of certain 

 bones, these being called fontanelles from the pulsation, or welling- 

 ip sensation, which can be felt there. They are six in number, 

 iwo being placed in the median line, anterior and posterior, and 

 two at either side, antero-lateral and postero-lateral. The anterior 

 fontanelle is situated between the antero-superior angles of the 



