1334 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



The epicranius and aponeurosis have been described elsewhere (p. 336). 



The pericranium differs from periosteum elsewhere in that it gives little 

 nourishment to the bone beneath, which derives most of its blood-supply from 

 the meningeal vessels. After necrosis of the skull there is no tendency to the 

 formation of an involucrum of new subperiosteal bone as in the long bones. 

 The pericranium is firmly adherent to the sutures of the skull bones, so that any 

 subpericranial effusion of blood or pus is limited by the sutures. 



Of the vessels of the scalp, the arteries, arising in the anterior region from 

 the internal, in the posterior from the external, carotid, are peculiar in their 

 position. Thus they lie superficial to the deep fascia, which is here represented 

 by the aponeurosis (fig. 1086). From this position arises the fact that a large 

 flap of scalp may be separated without perishing, as it carries its own blood- 

 vessels. From the density of the layer in which the vessels run they cannot 

 retract and are difficult to seize, haemorrhage thus being free. Finally, from 

 their position over closely adjacent bone, ill-applied pressure may easily lead to 

 sloughing. A practical point with regard to the veins is given below. The 

 lymphatics from the front of the scalp drain into the anterior auricular and 

 parotid, those behind into the posterior auricular, occipital and deep cervical 

 nodes. The nerves are derived from all three divisions of the trigeminus, from the 



Fig. 1086. — Section through the Scalp, Skull, and Dura Mater. (Tillaux.) 



Skin and superficial 



fascia with 

 hair bulbs and sebace- 

 ous glands 

 Fat pellets 



Epicranial aponeu- 

 rosis 

 Subaponeurotic 

 connective tissue 

 Pericranium 

 Subpericranial 

 connective tissue 



Skull: diploic tissue 



•Dura mater 

 Skull cavity 



facial (motor) and also from three branches of the second and third cervical. 

 The supply from the fifth explains the neuralgia in acute iritis, glaucoma, and 

 herpes frontalis, and also the pains shooting up from the front of the ear in late 

 cancer of the tongue. 



The emissary veins. — These are communications between the sinuses within, 

 and tlu; veins outside, the cranium. Most of them are temporary, corresponding 

 to the chief period of growth of the brain. Thus in early life, when the develop- 

 ment of the brain has to be very rapid, owing to the approaching closure of its 

 case, a free escape of blood is most essential, especially in children, with their 

 sudden explosions of laughter and passionate crying. 



The gravity of these emissary veins and their free communications with others 

 are shown by the reacUness with which they becorae the seat of thrombosis, and 

 thus of blood-poisoning, in cranial injuries, erysipelas, infected wounds of the scalp, 

 and necrosis of tlu; skull. They include the following: 



1. Vein throujjh the foramen cieciirn, bot,vveon the anterior extremity of the superior sagittal 

 sinus and the nasal mucous membrane. 'I'he vakie of this temporary outlet is well seen in the 

 timely profuse epistaxis of children. Othcsr more permanent communications between the skull 

 cavity and nasal mucous membrane pass through the ethmoid foramina. The fact that the 

 nasal mucous membrane is loose and ill-sui)i)orted on the nasal conch;e (turbinate bones) 

 allows its vessels to give way readily, and thus forms a salutary safeguard to the brain, warding 

 off many an attack of af)oplexy. 2'. Vein through the mastoid foramen, between the transverse 



