504 



THE SPINAL COED. 



dorsal or to the second lumbar vertebra. The position of the lower end of the cord also 

 varies according to the state of curvature of the vertebral column, in the flexion 

 forwards of which, as in the stooping posture, the end of the cord is slightly raised. 

 In the foetus, at an early period, the cord occupies the whole length of the vertebral 

 canal ; but, after the third month, the canal and the roots of the lumbar and sacral 

 nerves begin to grow more rapidly than the cord itself, so that at birth the lower end 

 reaches only to the third lumbar vertebra. 



Fig. 341. POSTERIOR VIEW OP THE MEDULLA OBLONGATA AND OP THE SPINAL CORD 

 WITH ITS COVERINGS AND THE ROOTS OF THE NERVES (from Sappey). 4 



The theca or dura-matral sheath has been opened by a median incision along the whole 

 length, and is stretched out to each side. On the left side, in the upper and middle parts 

 (A and B), the posterior roots of the nerves have been removed so as to expose the liga- 

 mentum denticulatum ; and along the right side the roots are shown passing out through 

 the dura mater. The roman numbers indicate the different nerves in the cervical, dorsal, 

 lumbar, and sacral regions : 9, several of the pointed processes of the ligamentum den- 

 ticulatum ; 10, origin of several posterior roots ; 11, posterior median fissure ; 12, 

 ganglia of the spinal nerves ; 13, part of the anterior roots seen on the left side ; 14, 

 the united nerve ; 15, tapering lower end of the spinal cord; 16, filum terminale; 17, 

 cauda equina. 



The length of the spinal cord is from fifteen to eighteen inches ; and it 

 varies in diameter in different situations. Its general form is cylindrical, 

 somewhat flattened before and behind. It presents two enlargements an 

 upper or cervical, and a lower or lumbar. The cervical enlargement is of 

 greater size and extent than the lower. It reaches from the third cervical 

 to the first dorsal vertebra ; its greatest diameter is from side to side. 



