176 THE SKELETON. 



and is formed by the junction of the frontal with the facial bones ; it extends 

 from the external angular process of one side, to the same point on the opposite 

 side, and connects the frontal with the malar, the sphenoid, the ethmoid, the 

 lachrymal, the superior ma'xillary, and the nasal bones on each side. 



The sutures remain separate for a considerable period after the complete 

 formation of the skull. It is probable that they serve the purpose of permitting 

 the growth of the bones at their margins ; while their peculiar formation, and 

 the interposition of the sutural ligament between the bones forming them, 

 prevents the dispersion of blows or jars received upon the skull. Dr. Humphry 

 remarks, " that, as a general rule, the sutures are first obliterated at the parts 

 in which the ossification of the skull was last completed, viz., in the neighbor- 

 hood of the fontanelles; and the cranial bones seem in this respect to observe 

 a similar law to that which regulates the union of the epiphyses to the shafts 

 of the long bones." 



THE SKULL. 



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. 



VERTEX OF THE SKULL. 



The Superior Eegion, or Vertex, presents two surfaces, an external and an 

 internal. 



The External Surface is bounded, in front, by the nasal eminences and super- 

 ciliary 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 backwards by the sagittal, which terminates 

 behind in the lambdoid. From before backwards 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 is the parietal foramen am 

 parietal eminence, and still more posteriorly the smooth convex surface of tin 

 occipital bone. 



The Internal Surface is concave, presents eminences and depressions for th( 

 convolutions of the cerebrum, and numerous furrows for the lodgment o: 

 branches of the meningeal arteries. Along the middle line of this surfaiv 

 longitudinal groove, narrow in front, where it terminates in the frontal ci 

 broader behind; it lodges the superior longitudinal sinus, and its margins aftbrc 

 attachment to the falx cerebri. On either side of it are several depressions foi 

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

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

 backwards, by the sagittal ; behind, by the lambdoid. 



BASE OP THE SKULL. 



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

 or cerebral, and an external or basilar. 



The Internal, or Cerd>r<tt Surface (Fig. 129), presents three fossae on each Bid 

 called the anterior, middle, and posterior f out* of the cranium. 



The Anterior Fossa is formed by the orbital plate of the frontal, the cribriform 

 plate of the ethmoid, the ethmoidnl process and lesser wing of the sphenoid. 

 It is the most elevated of the three fossae, convex externally where it corre- 



