SUTURES. 55 



and parietal bones, inclines downwards and outwards on each side and has 

 somewhat of the form of the Greek letter A. The occipito-mastoid suture 

 (additamentum suturce, lambdoidalis) is in continuation with it. 



The parietal, or sagittal suture, connects the two parietal bones : it is 

 continued in children, and not unfrequently in adults, by a suture between 

 the two halves of the frontal bone, the frontal suture. 



The spheno-parietal suture, the line of contact of the parietal bone and 

 great wing of the sphenoid, is about half an inch in extent. It is absent 

 only in very rare cases, and then the frontal and temporal bones come into 

 contact. 



The temporo-parietal suture consists of two very distinct parts, the 

 squamous suture, arched in direction, in which the scale-like margin of the 

 squamous portion of the temporal bone overlays the similar margin of the 

 parietal, and the parieto-mastoid suture (additamentum suturce squamosce), 

 which is thick and serrated. 



From the nature of the squamous suture, the inferior margins of the parietal bones 

 cannot be pressed outwards by forces acting either from above or from within, without 

 at the same time pushing before them the squamous margins of the temporals. 

 When the pars squamosa is thus acted on, it may either bulge outwards alone, or may 

 press downwards the base of the pars petrosa. Both phenomena are observable in 

 broad skulls. 



OSSA TRIQTTETRA. Supernumerary ossicles are found in a great number of skulls, 

 interposed between the cranial bones, like islets in the sutures. They are called ossa 

 triquetra, ossa Wormii, ossa suturamcm, &c. They are of irregular form, with margins 

 adapted to the character of the sutures in which they are situated. They are most 

 frequently found in the occipito-parietal suture, where they occur sometimes in great 

 numbers, more or less symmetrically arranged; in other instances, one or several bones 

 of considerable size may occupy the place of the superior part of the occipital. They 

 are less frequent in the parietal suture and at the anterior fontanelle, are found only 

 in small numbers in the fronto-parietal suturCj and rarely occur in the squamous. 

 A single triquetrous bone intervenes sometimes between the parietal and sphenoid ; 

 and still more frequently between the parietal and the place of meeting of the squamous 

 and mastoid portions of the temporal. 



GENERAL CONFORMATION OP THE SKULL. 

 THE EXTERIOR. 



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

 inferior, anterior, and lateral regions./ 



The SUPERIOR REGION, extending from the supra-orbital ridges iu ^ront to 

 the superior curved line of the occipital bone behind, and bounded laterally 

 by the temporal ridges, is smooth and convex, covered only by the muscular 

 fibres and fascia of the occipito-frontalis muscle and the integument. It is 

 of an oval form, broader in the parietal than the frontal region, flattened in 

 front, and projecting somewhat in the middle behind. 



The ANTERIOR REGION of the skull, below the forehead, presents the 

 openings into 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 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 nasal spine. Below the nasal aperture are the 

 incisor fossae of the upper jaw ; below the orbits are the canine fossae ; and 

 external to the canine fossae are the prominences of the cheeks, formed by 

 the anterior inferior parts of the malar bones. The lower jaw completes the 



