Method XX 1 1 1 



meninges. On the surface of the specimen look for parts of 

 the plexus venosus vertebralis left on after its removal from the 

 foramen spinale (vertebral canal). Attached at regular intervals 

 (segments) observe the thirty-one pairs (human) of Nn. spinales 

 and the small enlargement on each nerve, the ganglion spinale. 

 How do the ganglia differ in appearance from the rest of the 

 nerve ? Do they vary in size ? At what levels do the largest 

 occur? 



With scissors, on the dorsal side, longitudinally slit a portion 

 of the outer of the investing membranes, the dura mater spinalis, 

 and pin it back from both sides. Note a middle membrane, the 

 arachnoidea spinalis. Separating the arachnoidea spinalis from 

 the dura mater spinalis is the cavum subdurale. How are the 

 two membranes connected ? 



Closely investing the medulla spinalis, identify a third mem- 

 brane, the pia mater spinalis. Along the dorsal mid-line and 

 passmg through or dividing the cavum subarachnoideale, note 

 the septum subarachnoideale connecting the pia mater with the 

 arachnoidea. 



Observe the ligamenta denticulata performing the same office 

 along the lateral aspects of the medulla spinalis. Which of the 

 three investing membranes is the thickest ? Which the most 

 vascular? Make a sketch showing the relations of the mem- 

 branes to each other and to the medulla spinalis. Remove a 

 small piece of the dura mater and tease it under the dissecting 

 lens. What is its structure ? 



{V) Blood supply: On either side of the dorsal mid-line, note 

 the small arteriae spinales posteriores. The venae spinales poste- 

 riores are somewhat larger and usually course nearer the mid-line. 



Carefully remove a portion of the outer membranes so as to 

 expose a part of the ventral surface of the medulla spinalis, and 

 note the larger irregular Arteria spinalis anterior and the smaller 

 Venae spinales anteriores. Both the anterior and posterior 

 arteries are fed by small branches (the rami spinales) from the 

 larger arteries lying outside the vertebral column. How do the 

 rami spinales pass from the dura mater to the pia mater? 



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