THE HEAD 221 



the ophthalmic veins, and by this route venous blood may be 

 returned from the scalp to the cavernous sinus. 



In addition to those mentioned above> emissary veins con- 

 nect the superior sagittal (longitudinal) sinus with the veins of 

 the nasal mucous membrane through the foramen caecum, and 

 the cavernous sinus with the pterygoid venous plexus. Epi- 

 staxis is common in children during a fit of violent temper or of 

 crying, and it serves to reduce the intra-cranial blood-pressure. 

 In this way the emissary veins may act as safety valves. 



The Pericranium covers the outer surface of the skull and is 

 easily stripped off except at the sutures, where it is connected 

 with the endo-periosteal layer of the dura mater. The latter 

 provides the bones of the skull with their blood-supply, and on 

 this account removal of portions of the pericranium, in operations 

 for tuberculous periostitis of the skull, is not necessarily followed 

 by death of the exposed bone. A sub-pericranial haemorrhage, 

 or cephal-hccmatoma, is limited to the surface of some particular 

 bone by the inter-sutural membrane. It is probably due to the 

 rupture of some of the inter-sutural veins during the moulding 

 of the fcetal head, and can easily be distinguished from the 

 swelling produced by Caput Succedaneum, as the latter occurs in 

 the scalp and is not limited to the surface of any particular bone. 



The Developing Cranium expands rapidly to accommodate 

 itself to the rapidly growing brain. At first it consists of a 

 membranous capsule, but supporting cartilaginous bars soon 

 appear in its base. The bars become ossified, and at the same 

 time centres of ossification appear in the membrane to form the 

 parietal bone and the squamous portions of the temporal, 

 occipital, and frontal bones. In the regions of the anterior and 

 posterior fontanelles the membrane is the only covering of the 

 brain and its meninges at birth. The anterior fontanelle is 

 placed at the area where, in the adult, the coronal and sagittal 

 sutures meet, and through it the pulsations of the brain can 

 readily be seen and felt. It should be closed by the end of the 

 second year, but in rickets it is still widely open at that age. 

 When the intra-cranial pressure is raised, e.g. in crying, the 

 anterior fontanelle becomes tense, while it is sunken in con- 

 ditions of malnutrition and exhaustion. Faulty development 

 of the skull at the suture lines is accountable for the various 

 forms of meningoceles (p. 534). 



The cranial deformities produced by hydrocephalus (p. 226) 

 are determined by the condition of the sutures at the time of 



