744 



CRANIUM. 



portion of the bones themselves in part, convey 

 the force downwards, the former forwards 

 through the median line of the ethmoid to the 

 front of the sphenoid, and backwards through 

 the superior and inferior limbs of the crucial 

 spine of the occiput, traversing the foramen 

 magnum, and passing through the basilar 

 process to the back of the sphenoid bone : 

 the latter forwards through the frontal bone 

 to the small and great wings, and, through 

 them, to the body of the sphenoid ; and 

 backwards through the parietal and occipital 

 to the lateral limbs of the crucial spine. 

 The parietals convey it down the sides to 

 the great wing of the sphenoid and the mas- 

 toid process of the temporal bone, from which 

 it is transmitted to the common centre ; and 

 the slight rotation which is permitted to the 

 temporal bone, (and which has already been 

 alluded to,) materially tends to break the force 

 in its transit. Nor is there any imperfection in 

 this apparent inclination of the parietals to an 

 outward divergence, for the squamous process 

 of the temporal bone which overlaps each be- 

 tween its two fixed points is strongly supported 

 on its outer side by the temporal muscle. 



ABNORMAL CONDITIONS OF THE CRANIUM. 



Most of the abnormal conditions of the cra- 

 nium are dependent on circumstances con- 

 nected with the evolution of the brain, and 

 are mostly acquired after birth ; the only con- 

 genital variations being those in which there is 

 a total or a partial privation of its parietes. 



There is no vestige of it, or, indeed, of the 

 head itself, in the true acephalous foetus ; but, 

 whenever the medulla oblongata is present, the 

 base of the cranium is developed, and often- 

 times there are found rudimentary portions of 

 the other bones (false acephalia and anence- 

 phalia) . 



The parietal or occipital bones, and some- 

 times all of them are imperfect in that mal- 

 formation termed encephalocele, which, in 

 some cases, is analogous to spina bifida, and, 

 in others, to hernia cerebri. When serous fluid 

 constitutes the tumour, the deficiency of the 

 bones is considerable, owing to the arrestation 

 of the formative process ; but when the brain 

 protrudes, their development continues in such 

 a way as to embrace the root of the tumour, and 

 then the calvaria, flattened and in contact with 

 the base, exhibits an opening through which 

 the hernia escaped. 



The cranium is said to be, at times, insuffi- 

 ciently evolved; the evolution of its parts being 

 accelerated and their coalescence prematurely 

 effected, so that the ossific capsule is formed 

 before the brain has attained its full growth. 

 It is, however, most probable that in this as in 

 other cases it adapts itself to the brain, and 

 that it is on an imperfect development of that 

 organ that the smallness of the cranium is de- 

 pendent; but varieties of this description which 

 are connected with deficiences of mental en- 

 dowment will scarcely admit of enumeration. 



The parietes of the cranium may be preter- 

 naturally thin, without this l.eing dependent on 

 disease ; but they are most obviously in that 



condition in hydrocephalus, in which affection, 

 however, there are two opposite states of the 

 skull. 



When the disease occurs in infancy, and 

 persists for any length of time, the bones of 

 the calvaria usually become thin and pellucid ; 

 the spaces between -them are of great extent ; 

 and the deposition of the inorganic texture 

 is arrested in such a way that instead of 

 bones we have frequently little more than a 

 membrane- cartilaginous lamina, and some- 

 times not even that ; for instances have been 

 known in which the upper part of the head 

 has been covered by membrane only. This 

 suspension of action, however, is in some 

 instances only temporary. The deposition of 

 ossific matter becomes then more rapid and 

 abundant than under ordinary circumstances ; 

 the points of deposit are more numerous than 

 usual ; and a skull of gigantic dimensions and 

 of peculiar and premature hardness is pro- 

 duced. 



It has been sufficiently explained that the 

 several ossific elements of the cranium unite in 

 definite numbers to produce the bones which 

 we have been occupied in describing. Never- 

 theless, it not unusually happens that some of 

 these elements, or, otherwise, adventitious de- 

 posits of a similar character, which manifest 

 themselves, do not flow into and combine 

 with the other elements of the bone in which 

 they occur ; but, on the contrary, each in itself 

 forms the centre of an ossific process, and the 

 bone thus formed (be it large or small) articu- 

 lates by its circumference to the parts with 

 which it comes into contact. These adven- 

 titious pieces are commonly known under the 

 name of ossa Wormiana, because it is supposed 

 that they were first described by Wormius, a 

 physician at Copenhagen in the seventeenth 

 century ; * they are also called ossa triquetra, 

 triangularia, ossa suturarum, ossa supranume- 

 raria. They vary in situation, number, and 

 size. In general they are situated in the 

 lambdoidal suture ; they are, however, met with 

 in the sagittal, occasionally in the coronal, and 

 (though rarely) in the squamous suture. One 

 of the most remarkable is that which sometimes 

 replaces the superior angle of the occipital 

 bone, called by Blasius os triangulare or epac- 

 tale. Bertin describes one in the situation of 

 the anterior fontanelle. 



It is by a process analogous to the pre- 

 ceding that the occipital bone occasionally 

 presents a suture between the upper and under 

 halves of its posterior portion. The elements 

 of those two parts combine among themselves, 

 and the pieces resulting from their union ap- 

 proach, and, instead of forming the continuous 

 bone, as we usually see it, they are associated 

 by means of an additional suture. 



An anomaly of not very unusual occurrence 

 is the permanence of the suture uniting the 

 two halves of the frontal bone, and which is 

 seldom apparent beyond the second year of 

 extra-uterine life. 



* Vid. 01. Wormii et ad eum doctomm viriim 

 ppistolic, t. i. Hainire, 1728. 



