I470 



A MANUAL OF ANATOMY 



The centrifugal poles of the nerve-cells, issuing from the ganglion, represent 



the peripheral sensory fibres of the nerve. 



The vagal ganglion, which is broken up into the ganglion of the root and the 



ganglion of the trunk, is disposed to- 

 wards the sensory fibres of the vagus or 

 pneumogastric nerve as in the case of the 

 other ganglia. 



Neural Crest 



eural Tube 



, Spinal Ganglion 



Deyelopment of the Sympathetic 

 Nervous System. 



The sympathetic ganglia may be re- 

 garded as being developed from the 

 ventral aspects of the neural crests and 

 spinal ganglia, and they are therefore 

 of ectodermic origin, according to this 

 view. Certain cells become detached 

 from the neural crests and spinal ganglia, 

 and migrate ventralwards towards the 

 region of the aorta, where they form the 

 ganglionic sympathetic chain. The gang- 

 lionic cells proliferate and are furnished 

 with processes which become fibrillar. 

 These fibrillar processes give rise to the chain which connects the ganglia, and 

 also to the grey rami communicantes ajid the various visceral branches. 



Migratory Cells 

 from Ganglion 



Motor Root of 

 Spinal Nerve 



Sympathetic 

 Ganglion 



Aorta 



Fig. 614. — Development of Sym- 

 (schematic.) 



PATHETIC Ganglia. 



MENINGES OF THE ENCEPHALON. 

 Dura Mater. 



The dura mater is a strong fibrous membrane which surrounds 

 the encephalon, and is composed of two layers — outer and inner. 

 The outer or periosteal layer serves as the internal periosteum or 

 endocranium of the cranial bones, and the inner or sustentacular 

 layer supports the encephalon. It is more firmly adherent to the 

 bones fonning the base of the skull than over the cranial vault, and 

 it is also firmly attached along the course of the sutures. At the 

 various openings it is prolonged outwards, blending with the sheaths 

 of the transmitted nerves, and also becoming continuous with the 

 external periosteum or pericranium. At the sphenoidal fissure it 

 passes into the orbit to form the orbital periosteum. At the 

 lower margin of the foramen magnum the two layers of which 

 the dura mater is composed separate. The external layer blends 

 with the periosteum of the occipital bone around the margin 

 of the foramen magnum. The internal layer is prolonged into 

 the spinal canal, and forms the theca of the spinal cord. The outer 

 surface of the dura mater is rough and flocculent, owing to fibrous 

 processes which connect it to the inner surfaces of the cranial 

 bones. Its inner surface is smooth and covered by endothelium. 

 Superiorly, on either side of the superior longitudinal sinus, there 

 are several small granular nodules, called Pacchionian bodies, 

 which are best marked in old age. They indent the parietal bone, 

 and protrude into the superior longitudinal sinus, carrying with 

 them prolongations from the endothelial lining of the sinus, which 

 separate them from the blood. 



