THE CENTRAL NERVOUS SYSTEM. 337 



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

 or column of Burdach. 



The 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. FIG 



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

 siderable space. The dura mater is contin- THE'CERVICAL R 

 uous with the fibrous sheaths of the spinal GION. 



nerves at their points of exit. Along the *' P osterior median 



sulcus ; b, posterior 



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

 mater by a delicate strand of connective tissue 



probably equivalent to the " ligamentum <?, fasciculus cuneatus; 



...,,- /, white matter; g, 



denticulatum of man. gr ay matt er; A, cen- 



The arachnoid is a delicate cellular mem- tral canal - 

 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. 135. SECTION OF substance of the cord. The nerves pierce 

 SPINAL CORD. SHOWING + 

 THE ORIGIN OF A PAIR 



OF SPINAL NERVES. Spinal Nerves. From the spinal cord 



a, dorsal root; b, spinal arise the spinal nerves. Of these there 



ganglion; c, dorsal ramus; . . . , 



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

 tralroot - 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 



