CRANIUM. 743 



rence would be to strengthen the part in which shock on its summit. The parietal dome is 

 (from the situation of the organ) these vibra- placed with its summit (the parietal depression) 

 tions might, in general, be expected to concur; looking downwards and inwards. Below it 

 and this is the contrivance adopted in the era- is received on the extremities of the lateral 

 nium, for in the centre of its base there is a qua- ribs ; above, it thrusts against the remainder of 

 drilateral portion (the body of the sphenoid the longitudinal rib ; behind, it falls on the 

 bone) of characteristic massiveness and strength, corresponding portion of the horizontal arch- 

 il does not however augment uniformly in and, in front, it antagonizes the frontal, 

 its substance from above downwards. The It is by the bases of these domes thus 

 matter is accumulated in dense lines or ribs, thrusting against a solid frame-work, that the 

 which pass to a common centre, and constitute cranium is endowed with the power of re- 

 thereby a peculiar skeleton or frame-work of sisting lateral shocks whether they approach 

 surpassing strength, which admits of the intro- from before or behind ; and it is not, as some 

 duction of a lighter and more fragile structure allege, simply by the mobility of the head, 

 in the intervening spaces, and resists the shocks that it withstands blows, which, if it were 

 that arrive through the spine, from behind or fixed, would fracture it. 



from above. There yet remains to be noticed an impor- 

 This frame-work is situated almost entirely tant part of this skeleton or frame-work ; that 

 in the base; the only part which is in the which bears upon the spine, and resists the 

 calvarium being a longitudinal curved line, force transmitted through it. At the bottom of 

 formed by the ethmoidal process of the sphe- the pit containing the cerebellum, there is an 

 noid bone, the crista galli of the ethmoid, the elliptical opening (the foramen magnum), the 

 spine of the frontal, the thickened commutual margin of which is very dense; this opening is 

 margins of the parietals, and the superior limb provided underneath with two tubercles (the 

 of the internal occipital spine. Independently articulaling processes), by which it rests on the 

 of this curved rib, the calvarium consists of vertebral column; from these tubercles a curved 

 four ovoidal domes, two on each side; formed, rib on each side (the lateral process of the oc- 

 the anterior by the corresponding half of the cipital bone and the mastoid of the temporal) 

 frontal bone, and the posterior by the parietal, extends upwards and outwards to the extremity 

 The summits of these domes are their centres of the posterior lateral rib ; the segmenl of the 

 of ossification, and their bases abut, partly on margin of the opening which is anterior to the 

 the longitudinal rib, and partly on the frame- tubercles, is prolonged upwards and forwards, 

 work in the base. in the form of a broad pillar (the basilar pro- 

 The part to which all the forces tend is the cess), to ihe back part of the common centre; 

 body of the sphenoid bone. From its posterior the segment which is behind the tubercles 

 corners there pass backwards two ribs, (ihe sends off, al its back part, a spine (the inferior 

 petrous processes of the temporal bones,) limb of the internal crucial spine), which ends 

 which terminate on the extremities of an arch, at the centre of the horizontal arch, at the point 

 (the lateral limbs of the internal crucial spine where the superior longitudinal rib terminates; 

 of the occiput,) which is placed horizontally, and this point of confluence of the forces from 

 and the convexity of which is turned back- below, from above, and from behind, is strength- 

 wards, ened by a nodule (the internal occipital protu- 

 This arch and the two ribs which connect it berance). The frame- work of the cerebellar 

 to the centre are in the line in which the oc- cavity is thus connected with that of the general 

 ciput would strike the ground in falling back- cavity; anteriorly, to the body of the sphenoid 

 wards; and they further form the brim of the bone; posteriorly, to the tubercle of the occi- 

 pil which contains the cerebellum, so that the pital ; and, laterally, to the extremities of the 

 vibrations of force pass in the interstice between petrous processes of the temporal bones. In 

 that organ and the cerebrum. both of them it will be seen that they occupy 

 From each side of the body of the sphenoid spaces between the grand divisions of the ner- 

 bone there stretches forwards, outwards, and vous matter, which latter is, therefore, removed 

 upwards towards the temples, a curved rib, from the chance of sustaining injury by shocks, 

 (the anterior pait of the great wing,) and, from much more completely than it could have been 

 the anterior part of the body, a transverse rib had the parietes been submitted to a progres- 

 which overlays the former. These and the sive augmentation of substance from above 

 posterior lateral ribs, all of which depart from downwards. As it is, the spaces in which the 

 a common centre, constitute the frame-work of nervous matter reposes are thin and frequently 

 the base which sustains the ovoidal domes of diaphanous ; and, were they situated in un- 

 the calvaria. The frontal dome is placed with protected parts, would be perforated by the 

 its summit (the frontal depression) looking slightest force. 



backwards, downwards, and inwards ; its mar- During a considerable period of life the su3- 



gin is received, inferiorly on the whole length ject enjoys additional protection from the slight 



of the anterior transverse, and on the extremity yielding of the bones, and from the cartilage 



of the anterior lateral curved rib; towards the which intervenes especially at the base. Pres- 



middle line, on so much of the longitudinal sure applied on the vertex would tend to disjoin 



rib as extends to the parietal bones ; and supe- the parietal bones from each other, and from 



riorly, it is applied against a portion of the the frontal and occipital bones. This the pe- 



base of the parietal dome. It is against these culiar nature of the articulations forbids, and 



parts that it thrusts, whenever it receives a the longitudinal rib chiefly, and the expanded 



