150 SPECIAL ANATOMY OF THE SKELETON 



times found at the root of the nose, where a protrusion of the anterior horn of the lateral ventricle 

 takes place through a deficiency of the frontonasal suture. These malformations are usually 

 found in the middle line, and most frequently at the back of the head, the protrusion taking place 

 through the fissures which separate the four centres of ossification from which the tabular portion 

 of the occipital bone is originally developed (see page 73). They most frequently occur through 

 the upper part of the vertical fissure, which is the last to ossify, but not uncommonly through the 

 lower part, when the foramen magnum may be incomplete. More rarely these protrusions have 

 been met with in other situations than those above mentioned, both through normal fissures, as 

 the sagittal, lambdoid, and other sutures, and also through abnormal gaps and deficiencies at 

 the sides, and even at the base of the skull. Force may be responsible in a young person for 

 separating a suture. This accident, seldom met with even in the young, is only occasionally 

 encountered in older persons. 



Fractures of the skull may be divided into those of the vault and those of the base. Frac- 

 tures of the vault are usually produced by direct violence. This portion of the skull varies in 

 thickness and strength in different individuals, but, as a rule, is sufficientlv strong to resist a very 

 considerable amount of violence without being fractured. This is due to several causes the 

 rounded shape of the head and its construction of a number of secondary elastic arches, each 

 made up of a single bone; the fact that it consists of a number of bones, united at all events in 

 early life by a sutural ligament, which acts as a sort of buffer and interrupts the continuity of 

 any violence applied to the skull; the presence of arches or ridges, both on the inside and outside 

 of the skull; which materially strengthen it; and the mobility of the head upon the vertebral 

 column, which further enables it to withstand violence. The elasticity of the bones of the head 

 is especially marked in the skull of the child, and this fact, together with the wide separation of 

 the individual bones from each other, and the interposition between them of other and softer 

 structures render fracture of the bones of the head a very uncommon event in infants and quite 

 young children; as age advances and the bones become joined, fracture is more common, though 

 still less liable to occur than in the adult. Fractures of the vault may, and generally do, involve 

 the whole thickness of the bone; but sometimes one table may be fractured without any corre- 

 sponding injury to the other. Thus, the outer table of the skull may be splintered and driven into 

 the diploe, or in the frontal or mastoid regions into the frontal or mastoid cells, without any injury 

 to the internal table. And on the other hand, the internal table has been fractured, and por- 

 tions of it depressed and driven inward, without any fracture of the outer table. As a rule, in 

 fractures of the skull the inner table is more splintered and comminuted than the outer, and 

 this is due to several causes. It is thinner and more brittle; the force of the violence as it passes 

 inward becomes broken up, and is more diffused by the time it reaches the inner table; the 

 bone, being in the form of an arch, bends as a whole and spreads out, and thus presses the par- 

 ticles together on the convex surface of the arch i. e., the outer table and forces them asunder 

 on the concave surface or inner table; and lastly, there is nothing firm under the inner table to 

 support it and oppose the force. Fractures of the vault may be simple fissures or starred and 

 comminuted fractures, and these may be depressed or elevated. These latter cases of fracture 

 with elevation of the fractured portion are uncommon, and can only be produced by direct 

 wound. In comminuted fracture a portion of the skull is broken into several pieces, the lines 

 of fracture radiating from a centre where the chief impact of the blow was felt; if depressed, a 

 fissure circumscribes the radiating line, enclosing a portion of skull. If this area is circular, it 

 is termed a pond fracture, and would in all probability have been caused by a round instru- 

 ment, as a blackjack or hammer; if elliptical in shape, it is termed a gutter fracture, and 

 would owe its shape to the instrument which had produced it, as a poker. A fracture may take 

 place along the line of an ossified or partly ossified suture. When a surgeon explores the vault 

 of the skull through a wound he must not mistake a Wormian bone for a fragment produced by 

 a fracture. A Wormian bone which may lead to mistake is encountered at the anterior inferior 

 angle of the parietal bone. Wormian bones are most frequently found along the lambdoid 

 suture. 



Fractures of the base are most frequently produced by the extension of a fissure from the 

 vault, as in falls on the head, where the fissure starts from the part of the vault which first struck 

 the ground. Sometimes, however, they are caused by direct violence, when foreign bodies have 

 been forced through the thin roof of the orbit, through the cribriform plate of the ethmoid from 

 being thrust up the nose, or through the roof of the pharynx. Other cases of fracture of the base 

 occur from indirect violence, as in fracture of the occipital bone from impaction of the spinal 

 column against its condyles in falls on the buttocks, knees, or feet, or in cases where the glenoid 

 cavity has been fractured by the violent impact of the condyle of the mandible against it from 

 blows on the chin. 



The most common place for fracture of the base to occur is through the middle fossa, and 

 here the fissure usually takes a fairly definite course. Starting from the point struck, which is 

 generally somewhere in the neighborhood of the parietal eminence, it runs downward through the 

 parietal bone and the squamous portion of the temporal bone and across the petrous portion of 

 this bone, frequently traversing and implicating the internal auditory meatus, to the middle 



