i3o8 A MANUAL OF ANATOMY 



It forms a dense fibrous tube, known as the theca, which extends 

 from the margin of the foramen magnimi of the occipital bone to 

 the level of the second sacral vertebra. Inferiorly, where it has 

 become tapering behind the second sacral vertebra, the theca is 

 perforated by the filum terminale, and from this level the spinal 

 dura mater is prolonged downwards around the filum terminale, 

 with which it blends. Finally it is attached, along with the filum 

 terminale, to the back of the first coocygeal vertebra, where it is 

 incorporated with the periosteum. In this situation the spinal dura 

 mater is firmly fixed. 



The theca surrounds the spinal cord very loosely, and it is separ- 

 ated from the wall of the spinal canal by an interval, called the 

 epidural spaee {cavum epidurale B.), which is occupied by venous 

 plexuses and loose areolar tissue. 



Opposite the intervertebral foramina of each side the theca 

 presents a series of openings, which are arranged in two parallel 

 rows. The openings constituting each pair are placed side by side, 

 but are distinct from each other, and they transmit the ventral or 

 anterior and dorsal or posterior roots of the spinal nerves. Each 

 of these roots, as it makes its exit, receives a tubular sheath 

 from the margin of the corresponding thecal opening, and these 

 sheaths remain distinct as far as the spinal ganglion of the dorsal 

 root. Thereafter the contiguous sheaths fuse and form one sheath, 

 which blends with the sheath of the corresponding spinal nerve. 



The spinal dura mater is maintained in position by several con- 

 nections, (i) Superiorly it is fixed to the margin of the foramen 

 magnum of the occipital bone. (2) Opposite the body of the axis 

 it is firmly attached, anteriorly, to the posterior occipito-axial 

 ligament. (3) Below the level of the axis it is loosely connected, 

 anteriorly, with the posterior common ligament of the bodies of the 

 vertebrae by fibrous bands. (4) Laterally it is connected with the 

 sheaths of the spinal nerves by means of the tubular sheaths which 

 it gives to the ventral and dorsal nerve-roots. (5) Inferiorly it 

 blends with the periosteum over the back of the first coccygeal 

 vertebra through means of the filum terminale. Posteriorly it is 

 quite free from connections. 



The spinal dura mater differs from the cranial dura mater in the 

 following respects : (i) It is destitute of an outer or periosteal layer ; 

 (2) it does not send septa into the spinal cord; and (3) it does not 

 contain venous sinuses. 



Blood-supply of Spinal Dura Mater. — ^The arteries are derived 

 from (i) the spinal branches of the vertebral, intercostal, and 

 lumbar arteries; and (2) the lateral sacral arteries, which are 

 branches of the internal iliac trunk. 



Nerve-supply. — ^The nerves are partly spinal and partly sym- 

 pathetic. 



Lymphatic Vessels. — There are no lymphatic vessels, their place 

 being taken by perivascular lymph-spaces in connection with the 

 arteries. 



