THll CliNTRAL NERl^OUS SYSTEM. 



337 



Goll. The lateral and thicker is the fasciculus cuneatus (^) 

 or column of Burdach. 



T/w membranes of the spinal cord : 



The dura mater is a tough fibrous membrane directly con- 

 tinuous with the dura mater of the brain. It 

 differs from the dura mater of the brain in 

 two particulars: 



1. At the foramen magnum it splits into 

 two layers, one of which lines the bony 

 vertebral canal and forms its periosteum, 

 while the other covers the cord. 



2. It is separated from the cord by a con- 

 siderable space. The dura mater is contin- 

 uous with the fibrous sheaths of the spinal 

 nerves at their points of exit. Along the 5' po^te'-ior median 



^ ^ sulcus; l>, posterior 



sides of the cord it is connected to the pia lateral sulcus; r, an- 

 matcr by a delicate strand of connective tissue '"'"'' '""'""" '""^'"•'"^ 



Fig. 134. 



SI5CTION 



- Cross- 



OF THE. 



Si'iNAL Cord in 

 THE Cervical Re- 

 gion. 



(/. fasciculus gracilis; 

 i\ fasciculus cuneatus; 

 y, while matter; g, 

 gray matter; //, cen- 

 tral canal. 



probably equivalent to the " ligamentum 

 denticulatum ' ' of man. 



The arachnoid is a delicate cellular mem- 

 brane lying beneath the dura mater, between it and the pia 

 mater. It forms a continuous investment for the cord, is not 

 vascular, and is said not to dip into the fissures of the cord. 



The pia mater invests the cord closely and contains some 

 blood-vessels. It is a delicate membrane which dips into the 



fissures and sulci of the cord and is con- 

 nected to it by numerous strands of con- 

 nective tissue that pass from it into the 

 Fig. 155. — Section of substance of the cord. The nerves pierce 



SriNALCoRo. showing; 

 THE Origin of a Pair 

 OF Spinal Nerves. 



It. 



Spinal Nerves. — From the spinal cord 

 a, dorsal root; /'. spinal arise the spiual nerves. Of these there 



ganglion; c, dorsal rannis; , . 



d, ventral ramus ; e, ven- are about thirty-eight pairs in the cat. 

 ^''^^ '■°°'- Eight are cervical, thirteen thoracic, 



seven lumbar, three sacral, and seven or eight caudal. Those 

 leaving the cervical (Fig. 133, 5 8 and /) and lumbar (Fig. 

 136) enlargements are larger than the others. The first 

 cervical nerve leaves the vertebral canal through the atlantal 



