736 



CRANIUM. 



ment which obtains in the frontal and occipital 

 bones ; that is, they are overlapped in the 

 upper part, while in the lower they overlap 

 those bones ; the inferior is sharp, and merely 

 terminates the articular surface already al- 

 luded to. 



The angles contained within these borders 

 are the Jrontal (which is nearly a right angle) 

 formed by the superior and anterior borders ; 

 the occipital (more obtuse) by the superior 

 and posterior borders ; the mastoidal, truncated 

 and articulated with the mastoid process of the 

 temporal bone; and the sp'mous (acute) re- 

 ceived on the tip of the great wing of the 

 sphenoid, and intervening between the tem- 

 poral and frontal bones. The mastoidal angle 

 is, on its inner surface, traversed by a sulcus 

 (the sulcus laterals) to lodge the lateral sinus 

 and to transmit it from the occipital to the 

 temporal bone. The spinous angle is deeply 

 grooved on its inner surface by the sulcus 

 spinosus for the middle meningeal artery, or 

 the arteria spinalis dura matris ; this groove 

 has its place frequently supplied by a canal, 

 then called canalis spinosus. 



Its connexions are with its fellow above ; 

 the temporal and sphenoid below ; the frontal 

 before; and the occipital behind. 



The parietal, like each half of the frontal 

 bone, is developed from the protuberance ; and 

 from this point the ossific matter radiates to- 

 wards its several borders. While this process 

 is going on, the part above and the part below 

 the centre form a considerable angle with 

 each other ; but this is much effaced when the 

 edges have arrived at their destination, espe- 

 cially when the squamous process of the tem- 

 poral quits its vertical for its curved position. 



Articulation of the cranial bones. These 

 several bones are locked together so as to form 

 the envelope of the brain, and the mode by 

 which their secure adherence to each other is 

 effected, differs in the summit, on the sides, 

 and in the base of the cranium. 



In the calvaria they are united either by the 

 overlapping or by the dove-tailing of their 

 edges, or else by the two modes combined. 

 The inner table does not proceed so far as the 

 external, and the latter being jagged with pro- 

 cesses which have no definite form, but which 

 are either tortuous, or narrower at their fixed 

 than at their free extremity, the outer tables 

 are immovably joined by the fixation of the 

 processes of each side into the spaces of the 

 other. By this means the inner tables of the 

 two bones are brought nearly into contact, 

 a thin lamina only of cartilage intervening ; 

 so that on looking into the vault, but little 

 more than a plain line will be noticed. Here, 

 however, there is no overlapping of the outer 

 tables ; but the only instance of it is in the 

 junction of the two parietals on the median 

 line, by which, in effect, they form but one 

 bone. On the sides of the skull there is a 

 mere overlapping of the descending by the 

 ascending portions, and to accomplish this, 

 and yet maintain uniformity of surface, those 

 parts of the outer tables which project beyond 

 the inner are pared off or thinned in opposite 



directions. Thus the squamous processes of 

 the temporal bones and the great wings of the 

 sphenoid rise upwards from a fixed basis and 

 form a wall which is bevelled off" on the inner 

 edge of its outer plate, so as to receive the 

 parietal and frontal bones, the outside of 

 which sustains a corresponding bevelling, by 

 which arrangement they are prevented from 

 being thrust outwards. The articulation of 

 the anterior and the posterior with the middle 

 portion of the calvaria, is a modification of 

 the two preceding; that is, the outer table is 

 partly bevelled and partly denticulated. The 

 frontal and occipital bones are symmetrical 

 and single, while there are two parietal ; and, 

 though these are well united by their mutual 

 interchange of denticulation, they are yet more 

 firmly consolidated by the extension of the 

 frontal and occipital bones on the frontal and 

 occipital angles of the parietals, and on their 

 borders to some distance from those angles ; 

 each symmetrical bone thereby forming a spe- 

 cies of cramp on the parietals. The edges, 

 however, of the outer tables are not pared to 

 a sharp ridge, but there is left sufficient to be 

 fashioned into processes to maintain the secu- 

 rity of the skull in a longitudinal direction. 

 The parietals being thus firmly secured above 

 and below, the intervening portion of their 

 edges is competent to act as girders themselves, 

 and, in fact, we find that the lower part of 

 their anterior and posterior borders overlap the 

 corresponding portions of the frontal and occi- 

 pital bones respectively. 



In the base of the cranium the bones are 

 placed in simple contact, and are so disposed 

 that forces, descending from above, will neces- 

 sarily drive them closer to each other. To 

 understand this rightly, we must suppose the 

 sphenoid and occipital to form (which, in fact, 

 they do) but one bone at an early period of 

 life. The temporal bone is placed alongside 

 the occipital, in such a way that the petrors 

 process is wedged into the angle between the 

 basilar process of the occipital, and the great 

 wing of the sphenoid ; while the latter, again, 

 is wedged into the angle between the petrous 

 and squamous processes of the temporal bone. 

 It has been said that on the upper surface of 

 the outer margin of the great wing, rests the 

 lower part of the squamous process ; in case 

 of force descending through the parietal bone 

 this will be the fulcrum, and the lever (the 

 squamous process) being directed outwards, 

 the mastoid and petrous processes will neces- 

 sarily be squeezed more forcibly against the 

 occipital bone and its basilar process. 



The peculiar appearance presented by the 

 articulations on the outer surface of the cal- 

 varia, has procured for them the name of 

 sutures, a term which is applied frequently to 

 the joinings in the base, although they are 

 essentially different in appearance and in fact. 

 Those which are situated in the calvaria, and 

 to which the name is more suitable, are the 

 coronal, lambdoidal, and sagittal sutures. 



The coronal suture extends between the two 

 great wings of the sphenoid bone across the 

 upper part of the skull, and 'connects the fron- 



