Section 3. 



Spinal Cord. 



The spinal cord extends from the atlas to about the second or 

 third sacral vertebra, and is completely enclosed in a dense 

 membrane, the dura mater. The canal in which it is lodged 

 is very much larger than the cord, especially at those parts 

 where the greatest amount of movement occurs, as in the neck. 

 The cord is not the same shape nor the same size throughout ; 

 oval in the cervical region, it becomes circular in the dorsal, and 

 again oval in the lumbar portion. It is largest where any con- 

 siderable bulk of nerves is being given off, and thus there is an 

 enlargement corresponding to the fore, and another to the hind 

 limbs (Fig. 136). On exposing the spinal canal, a large number 

 of nerves are found to be passing through the dura mater either 



<S> 



A B C 



Fig. 136. — Transverse Section of Spinal Cord of Horse. 



A, At level of first dorsal vertebra ; B, at level of first lumbar vertebra : 

 C, at level of first sacral vertebra. 



outwards or inwards, and these gain an exit from or entrance to 

 the spinal canal by means of the foramen formed at the junction 

 of the vertebrae. 



Spinal Nerves. — These are given off from or enter the cord 

 from the first bone of the neck to the fourth or fifth sacral 

 vertebra. A bunch of nerves passes through every intervertebral 

 foramen on each side, and this represents the spinal nerves. 

 When the dura mater of the cord is opened, it is observed that 

 the nerves, after entering this cover, divide into two groups : 

 one passes to the dorsal, the other to the ventral, aspect of 

 the cord. These are the superior and inferior roots of the 

 spinal nerves, or, to maintain the preferable nomenclature, the 

 dorsal and ventral roots. In the horse the dorsal and ventral 

 roots enter the cord, not as a single bundle, but as several. 

 On the dorsal root a nodule is found where the nerve passes 

 through the intervertebral foramen. This is the spinal ganglion, 

 and it is limited to the dorsal root. In the horse each of the 

 various rootlets possesses its ganglion (Fig. 139). There is" no 



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