THE BASE OF THE SKULL. 103 



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 surfaces, an external and an 

 internal. 



The external surface 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. 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, and is represented by a line drawn vertically 

 upward from the external auditory meatus, the head being in its normal position. 

 The point of junction of the sagittal and lambdoid sutures is called the lambda, 

 and is about 2| inches above the external occipital protuberance. From before 

 backward may be seen the frontal eminences and remains of the suture connect- 

 ing 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 fora- 

 men 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 surface is concave, presents depressions for the convolutions of 

 the cerebrum, and numerous furrows for the lodgement of branches of the menin- 

 geal 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 attach- 

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

 Pacchionian bodies, and at its back part the internal openings of the parietal 

 foramina. This surface is crossed, in front, by the coronal suture ; from before 

 backAvard by the sagittal ; behind, by the lambdoid. 



The Base of the Skull. 



The Inferior Region, or Base of the Skull, presents two surfaces an internal 

 or cerebral, and an external or basilar. 



The internal or cerebral surface (Fig. 71) presents three fossae, called the 

 anterior, middle, and posterior fossae of the cranium. 



The Anterior Fossa is formed by the orbital plates of the frontal, the cribri- 

 form 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. It is the most elevated 

 of the three fossae, convex externally where it corresponds to the roof of the orbit, 

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

 It is traversed by three sutures, the ethmo-frontal, ethmo-sphenoidal, and fronto- 

 sphenoidal, and lodges the frontal lobe of the cerebrum. It presents, in the 

 median line, from before backward, the commencement of the groove for the 

 superior longitudinal sinus and the frontal crest for the attachment of the falx 

 cerebri ; the foramen ccecum, an aperture formed between the frontal bone and the 

 crista galli of the ethmoid, which, if pervious, transmits a small vein from the nose 

 to the superior longitudinal sinus ; behind the foramen caecum, the crista galli, the 

 posterior margin of which affords attachment to the falx cerebri ; on either side of 

 the crista galli, the cribriform plate, which supports the olfactory bulb, and 



