208 THE SKELETON. 



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 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 breffma, and is represented by a line drawn vertically upward from the exter- 

 nal auditory meatus, the head being in its normal position. The point of junc- 

 tion 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 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 to this region the name of obelion is sometimes -given. 



The internal surface is concave, presents eminences and depressions for the 

 convolutions of the cerebrum, and numerous furrows for the lodgment 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 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 

 backward 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. 172) 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 olfactory groove, which supports the bulb of the olfactory 



