224 THE SKELETON. 



maxillary bone, which 'forms the inner boundary of the orbit. At the point of junction of the 

 lower margin of the orbit with the nasal process is to be felt a little tubercle of bone, which can 

 be plainly perceived by running the finger along the bone in this situation. This tubercle serves 

 as a guide to the position of the lachrymal sac, which is situated above and behind it. 14. The 

 outline of the lower jaw is to be felt throughout its entire length. Justin front of the tragusof 

 the external ear, and below the zygomatic arch, the condyle can be made out. When the mouth 

 is opened this prominence of bone can be perceived advancing out of the glenoid fossa on to the 

 eminentia articularis, and receding again when the mouth is closed. From the condyle the pos- 

 terior border of the ramus can be felt extending down to the angle. A line drawn from the con- 

 dyle to the angle would indicate the exact position of this border. From the angle to the 

 symphysis of the chin the lower, rounded border of the body of the bone is plainly to be felt. 

 At the point of junction of the two halves of the bone is a well-marked triangular eminence, the 

 mental process, which forms the prominence of the chin. 



Surgical Anatomy. An arrest in the ossifying process may give rise to deficiencies or 

 gaps ; or to fissures, which are of importance in a medico-legal point of view, as they are liable 

 to De mistaken for fractures. The fissures generally extend from the margin toward the centre 

 of the bone, but gaps may be found in the middle as well as at the edges. In course of time 

 they may become covered with a thin lamina of bone. 



Occasionally a protrusion of the brain or its membranes may take place through one of these 

 gaps in an imperfectly developed skull. When the protrusion consists of membranes only, and 

 is filled with cerebro-spinal fluid, it is called a meningoce 1c ; when the protrusion consists of brain 

 as well as membranes, it is termed an encephalocele ; and when the protruded brain is a prolonga- 

 tion from one of the ventricles, and is distended by a collection of fluid from an accumulation in 

 the ventricle, it is termed an hydrencephnlocele. This latter condition is frequently 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 fronto-nasal 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 

 is originally developed (see page 167). 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 two 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. 



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 sufficiently 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 spine 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 indi- 

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

 renders 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 correspond- 

 ing 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 

 particles 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 instrument, as a life-preserver or hanimer; 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. 



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



