THE SKULL AS A WHOLE 123 



be traced. The obliteration of the sutures takes place sooner on the inner than 

 on the outer surface of the skull. The sagittal and coronal sutures are, as a rule, 

 the first to become ossified the process starting near the posterior extremity of 

 the former and the lower ends of the latter. 



THE SKULL AS A WHOLE. 



The skull, formed by the union of the several cranial and facial bones already 

 described, when considered as a whole is divisible into five regions a superior 

 region or vertex, an inferior region or base, two lateral regions, and an anterior 

 region, the face. 



The Vertex of the Skull. The superior region, or vertex, presents two sur- 

 faces, an external and an internal. 



Surfaces. The external surface (nor ma verticalis) is bounded, in front, by the 

 glabella and supraorbital ridges; behind, by the occipital protuberance and superior 

 curved lines of the occipital bone; laterally, by an imaginary line extending from 

 the outer end of the superior curved line, along the temporal ridge, to the external 

 angular process of the frontal bone. This surface includes the greater part of 

 the vertical portion of the frontal, the greater part of the parietal, and the superior 

 third of the occipital bone; it is smooth, convex, of an elongated oval form, crossed 

 transversely by the coronal suture, and from before backward by the sagittal, 

 which terminates behind in the lambdoid. The point of junction of the coronal 

 and sagittal sutures is named the bregma. The point of junction of the sagittal 

 and lambdoid sutures is called the lambda, and is about 2f inches (7 cm.) above 

 the external occipital protuberance. From before backward may be seen the 

 frontal eminences and remains of the suture connecting the two lateral halves of 

 the frontal bone; on each side of the sagittal suture are the parietal foramen and 

 parietal eminence, and still more posteriorly the convex surface of the occipital 

 bone. In the neighborhood of the parietal foramen the skull is often flattened, 

 and the name of obelion is sometimes given to that point of the sagittal suture 

 which lies exactly opposite to the parietal foramen. 



The internal or cerebral surface is concave, presents depressions for the convolu- 

 tions of the cerebrum, and numerous furrows for the lodgement of branches of the 

 meningeal arteries. Along the middle line of this surface is a longitudinal groove, 

 narrow in front, where it commences at the frontal crest, but broader behind, 

 where it lodges the superior longitudinal sinus, and by its margin affords attachment 

 to the falx cerebri. On either side of it are several depressions for the arachnoid 

 villi, and at its back part the internal openings of the parietal foramina. This 

 surface is crossed, in front, by the coronal suture; from before backward by the 

 sagittal; behind, by the lambdoid. 



The Base of the Skull (the Skull being without the Mandible). The 

 inferior region, or base of the skull, presents two surfaces an internal or cerebral, 

 and an external or basilar. 



Surfaces. The internal or cerebral surface (Fig. 94) presents three fossae, called 

 the anterior, middle, and posterior fossae of the cranium. 



The anterior fossa (fossa cranii anterior) (Fig. 94) is formed by the orbital plates 

 of the frontal, the cribriform plate of the ethmoid, the anterior third of the superior 

 surface of the body, and the upper surface of the lesser wings of the sphenoid bone, 

 and is situated at a higher level than the other fossae. It is the most elevated of the 

 three fossa?, convex externally where it corresponds to the roof of the orbit, con- 

 cave in the median line in the situation of the cribriform plate of the ethmoid. 

 It is traversed on either side by three sutures, the ethmofrontal, ethmosphenoidal, 

 and frontosphenoidal, and lodges the frontal lobes of the cerebrum. It presents, 



