98 OSTEOLOGY. 



portion, formed by tlie junction of the mastoid part of the temporal with the occi- 

 pital, is called the masto-occipital. Between the bones forming the petro-occipital 

 suture, a thin plate of cartilage exists ; in the masto-occipital is occasionally found 

 the opening of the mastoid foramen. Between the outer extremity'of the basilar 

 suture and the spheno-parietal an irregular suture may be seen, formed by the union 

 of the sphenoid with the temporal bone. The inner and smaller portion of this 

 suture is termed the petro-sphenoidal ; it is formed between the petrous portion of 

 the temporal and the great wing of the sphenoid : the outer portion, of greater 

 length, and arched, is formed between the squamous portion of the temporal and 

 the great wing of the sphenoid : it is called the squamo-sphenoidal. 



The cranial bones are connected with those of the face, and the facial bones with 

 each other, by numerous sutures, which, though distinctly marked, have received 

 no special names. The only remaining suture deserving especial consideration is 

 the transverse. This extends across the upper part of the face, 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 

 maxillary, and the nasal bones on each side. 



The sutures remain separate for a considerable period after the complete forma- 

 tion 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. Mr. 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 neighborhood 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 Region 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 are the parietal foramen and parietal eminence, and still more pos- 

 teriorly the smooth convex surface of the occipital bone. 



The Internal Surface is concave, presenting 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 terminates in the frontal crest : broader behind ; 

 it lodges the superior longitudinal sinus, and its margins afford 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 backwards, by the 

 sagittal ; behind, by the lambdoid. 



