Chap. 27.] Spinal Marrow. 277 



ever, is here placed without ; the cineritious is placed 

 within, and by a tranfverfe fection of the medulla 

 fpinalis it appears to be in the form of a horfe-fhoe, 

 the convex fide of which is turned forwards and its 

 extremities backward. 



The fpinal marrow is inverted both with the dura 

 and pia mater. The former of thefe in pafiing out of 

 the foramen of the os occipitis, forms a kind of funnel, 

 adhering at its upper part to the ligamentary fubftance 

 which lines the bony canal of tjie vertebras. Lower 

 down there is no adhefion, except where the nerves 

 pals through the notches of the fpine, where the dura 

 mater, which invefts the medulla fpinalis, fends out on 

 each fide the fame number of meaths as there are gang- 

 lions and nervous trunks. 



The pia mater is connected with the dura mater by 

 means of a thin tranfparent fubftance, which from its 

 indentations between the fpinal nerves has been named 

 the ligamentum denticulatum. Its ufe is to fupport 

 the medulla fpinalis, that it may not affect the medulla 

 oblongata, or fpinal nerves by its weight, The lower 

 end of the ligamentum denticulatum runs to the os 

 coccygis far below the termination of the fpinal mar- 

 row. 



Each lateral portion of the medulla fpinalis fends 

 off, both from the fore and back parts, flat fafciculi of 

 nervous fibres. The anterior and pofterior fafciculi 

 are feparated from each other by the ligamentum den- 

 ticulatum ; then pafiing outwards they proceed through 

 the dura mater by two diftinct openings very near each 

 other. Having penetrated the dura mater, the pof- 

 terior bundle forms a ganglion, from the oppofite end 

 of which the trunk comes out again, and is there joined 

 by the anterior bundle. 



The membrana arachnoides is here very diftincl: 

 T 3 from 



