238 LABORATORY MANUAL OF HUMAN ANATOMY 



It will be well also to remove the posterior wall of the spinal canal in the 

 sacrum and coccyx. 



The cord lying in its external covering, the dura mater, or 

 pachymeninx spinalis, is now exposed. Notice the interspace 

 between the third and fourth lumbar vertebrae. This is the site 

 of Quincke 's ' ' lumbar puncture. ' ' Here a needle can be intro- 

 duced into the cavum subarachnoideale during life without 

 danger. 



Read carefully the description of the veins of the spinal 

 column and study Spalteholz, Figs. 493 and 494. 



Examine carefully 



(a) Spinal ramus of posterior ramus of each intercostal artery (ramus 

 spinalis rami post. A. intercostalis) , passing through an interver- 

 tebral foramen. (Cf. Spalteholz, Fig. 462.) 



(&) Spinal ramus of posterior ramus of each lumbar artery (ramus spi- 

 nalis rami post. A. lumbalis). 



(c) Spinal rami of vertebral artery (rami spinales A. vertebralis) and 

 the spinal rami of the ascending cervical artery (rami spinales A. 

 cervicalis ascendentis ) . 



Spinal Meninges. (Fig. 98.) 



Clean the external surface of the dura mater, removing fat 

 and areolar tissue. Lift the dura gently with fine forceps, and, 

 with fine, sharp scissors, cut through the dura mater spinalis in 

 the middle line .throughout its whole length. Take great care 

 not to injure the spinal arachnoid (ar.achnoidea spinalis). Trace 

 the terminal thread of the dura mater (filum durae mat r is spi- 

 nalis) to its bony attachment. Note that the dura mater spinalis 

 corresponds to the inner layer of the dura mater encephali, the 

 outer layer having fused with the periosteum of the vertebral 

 canal. The space (cavum epidurale) between the lining of the 

 vertebral canal and the dura mater spinalis contains the plexus 

 venosi, which in turn correspond to the cerebral sinuses. Note 

 disproportion between the size of the cord and the size of the 

 dura mater, especially in the regions where the mobility of the 

 vertebral column is great. Observe the fibrous filaments from 

 the anterior middle line of the dura which run obliquely down- 

 ward ventralward to be inserted into the ligamentum longitudi- 

 nale posterius; note their excessive development and fusion 

 from the fourth lumbar vertebra downward; this is the liga- 

 mentum sacrodurale anterius (ligament sacre anterieur of Tro- 

 lard). (Cf. Poirier et Charpy, iii., Fig. 77.) What is its 

 function? Note the dural sheaths of the nerve roots. 



