PRACTICAL CONSIDERATIONS : THE SKULL. 235 



infundibulum ends blindly, there is less likelihood of inflammation spreading from 

 the frontal sinus to the antrum. The nasal bones and their junction with the nasal 

 cartilages are easily recognized. The ramus and body of the lower jaw are to be 

 examined from the outside. The head and coronoid process are felt more easily if 

 the mouth be opened. 



PRACTICAL CONSIDERATIONS. 



The Cranium. — In the development of the cranium, provision is made for its 

 continuous enlargement, so that it may accommodate the rapidly growing brain. 

 Accordingly, the hrst rudiment is a membranous capsule, at the base of which carti- 

 lage is soon formed, giving support to the overlying portions. Then several centres 

 of ossification appear in various portions of the membrane and grow quicklv, so as 

 to protect the cerebral mass, the membrane remaining between these centres still 

 permitting the growth and expansion of the contents. Finally, the separate bones 

 become united, first at their edges, then at their angles, to make the complete 

 unyielding bony cranium. 



Arrest of these processes at various stages produces the equally various forms 

 of malformation, only a few of which need be mentioned here. It is to be observed 

 that, as a rule, they affect that part of the cranium that is of membranous origin, the 

 base (developed from cartilage) being much more rarely involved. Turner (quoted 

 by Allen) states that this is because the areas of the different bones are less precisely 

 defined, and because the process of ossification is more liable to disturbance in mem- 

 brane than in cartilage. 



In some cases the whole calvaria may be lacking and represented only by a 

 membrane. Fissures extending from the margins of the bones towards the centres 

 may exist, especially in the frontal and parietal bones, and may be mistaken for 

 fractures. Other irregular gaps filled with membrane may be found, and are gen- 

 erally situated at or near the natural foramina for vessels. The ossification of the 

 bones may be so incomplete as to constitute what is called aplasia cranii C07ige7iita, 

 a condition in infants due, usually, to maternal cachexia, and characterized by the 

 absence of bone either in localized patches or at points scattered over the entire 

 calvaria. * 



The non-closure of the sutures, or defective development, may be followed by 

 protrusion of the dura mater, either with or without part of the brain, constituting a 

 meningocele if the protrusion consists only of the membranes and cerebro-spinal 

 fluid ; an encephalocele if it contains brain ; or a hydreiicephalocele if the contained 

 brain is distended by an excess of ventricular fluid. 



These protrusions, in the order of frequency, occur (a) in the occipital region ; 

 (<5) at the fronto-nasal junction ; (r) in the course of the sagittal, lambdoidal, and 

 other sutures ; ('«') at the anterior or lateral fontanelles, and at the base of the cranium, 

 entering the orbit, nose, or mouth through normal or abnormal openings. 



In hydrocephalus there are practically always atrophy and thinning of the 

 cranium. "The deformities of hydrocephalus are largely determined by the con- 

 dition of the sutures at the time of the occurrence of the disease. Fixation at the 

 line of the sagittal suture causes bulging at the forehead and the occiput. Fixation 

 at both the lambdoidal and the sagittal sutures causes vertical bulging at the line of 

 the coronal suture and enormous increase of the ascending portion of the frontal 

 bone. Should the intracranial pressure announce itself prior to the closure of any 

 of the sutures of the vertex, the several bones composing it become widely separated 

 and the fontanelles enormously increased in size" (Allen). 



In microcephalus there is diminution in the size of the cranium and of its cavity, 

 due to premature ossification of the sutures. The subjects of microcephalus are 

 usually idiotic. The operation of "linear craniotomv," by which a strip of bone is 

 excised on either side of the median line of the cranium, was intended to permit of 

 the expansion of the brain in such cases. It has not established itself in surgical 

 favor. The arrested growth of the skull is thought to be due to the arrested 

 development.of the brain, and not vice versa. The skulls of idiots, even when not 

 markedly microcephalic, approximate in many ways to those of the lower animals. 



