62 THE SKULL AS A WHOLE. 



each lateral half, less so above where the frontal bone overlaps the parietal, and quite 

 simple at the lower end where the parietal overlaps the frontal ; inferiorly is the 

 temporo-paridal suture, consisting of two parts, the squamous suture, arched in form, 

 in which the squamous part of the temporal overlaps the parietal, and the parieto- 

 mastoid, short and serrated ; while at the antero-inferior angle is the short spheno- 

 parietal suture, about, half an inch in length, absent only in rare cases when the 

 frontal and temporal bones come into contact. 



The cranial sutures are conveniently arranged in three groups, a median longitudinal, a 

 lateral longitudinal and a vertical transverse. The first consists of the sagittal suture, which 

 is continued in the infant, and frequently in the adult, by the frontal suture ; in the lateral 

 longitudinal are included, on each side, the fronto-nasal, fronto-maxillary, fronto-lachrymal, 

 fronto-ethmoidal, fronto-malar, fronto-sphenoidal, spheno-parietal, squamous, and parieto- 

 mastoid sutures ; the third comprises the coronal and spheno-squamous, the lambdoid and 

 occipito-mastoid sutures ; and into this group also would fall the transverse articulations in the 

 centre of the base between the ethmoid, sphenoid and occipital. 



After adult life is reached the bones of the skull evince a disposition to unite, and many of 

 the sutures thereby become closed ; but the period at which this commences, as also the order 

 in which it proceeds, are subject to great variations, so that the condition of the sutures 

 affords very little assistance in determining the precise age of a skull. The process com- 

 mences generally about thirty years of age ; the union takes place first on the inner 

 surface, and frequently the large sutures are quite obliterated internally while they are 

 perfectly distinct on the external surface. The earliest points to close are commonly the 

 part of the sagittal suture between the parietal formina, and the lower ends of the coronal 

 suture ; the more dentated parts of these sutures and the lambdoid follow later. The 

 squamous is very late in closing, and it is noteworthy that when the frontal suture fails to 

 unite at the usual time it may remain unchanged even to very advanced age. (Dwight, 

 " The Closure of the Cranial Sutures as a Sign of Age," Boston Med. and Surg. Journ., 

 April, 1890.) 



"Wormian bones. Ossa triquetra, ossa sutiirarum. These are irregular ossifications, 

 found in many skulls, interposed between the cranial bones ; seldom in the face. They are 

 of irregular form, with margins adapted to the character of the sutures in which they are 

 situated, and usually of small size ; but they may exceed an inch in diameter. Their most 

 frequent seat is in the occipito-parietal suture, where they sometimes occur in great numbers, 

 more or less symmetrically arranged : in some cases one or several bones of considerable size 

 occupy the place of the superior part of the occipital, more rarely of the antero-superior angles 

 of the parietal bones : a scale-like ossification is often seen between the antero-inferior angle 

 of the parietal and the great wing of the sphenoid (epijpterfo lone, Flower). They are much 

 less frequent in the other sutures. 



EXTERNAL SUBFAOB OF THE SKULL. 



The external surface of the skull may be conveniently divided into superior, 

 inferior, anterior, and lateral regions. 



The superior region, extending from the supraorbital margins in front to the 

 superior curved lines of the occipital bone behind, and bounded laterally by the 

 temporal lines, is smooth and convex, covered only by the integument and by the 

 muscular fibres and aponeurosis of the occipito-frontalis muscle. The skull as seen 

 from above is of an oval form, broader in the parietal than the frontal region, 

 flattened in front, and projecting somewhat in the middle behind. There is also a 

 slight projection from the general curve at each of the frontal and parietal 

 eminences. 



The anterior region of the skull, below the forehead, presents the openings of 

 the orbits, bounded by the frontal, malar, and superior maxillary bones ; and between 

 the orbits, the bridge of the nose, formed by the nasal bones and ascending processes 

 of the superior maxillaries. Below the nasal bones is the anterior nasal aperture, of 

 an inverted heart-shape : its thin margin gives attachment to the nasal cartilages, 

 and projects forwards in the middle line below as the anterior nasal spine. Below 

 the nasal aperture are the incisor fossas of the upper jaws ; below the orbits are the 



