276 ANATOMY OF THE DOMESTIC FOWL 



cylindrical cord, flattened from above downward. It extends from 

 the foramen magnum at the base of the medulla to the caudal portion 

 of the spinal canal where it terminates in a fine filament. In order 

 to allow considerable motion of the spinal column without danger of 

 injury to the spinal cord, the cord is loosely suspended in the canal. 

 The meninges, or coverings, are continued from the brain. In addi- 

 tion to these there are to be found arteries, veins, and nerves en- 

 tering and others making their exit .from the canal and from the 

 cord. At the cervico-dorsal juncture, where the brachial plexus 

 is given off, the cord is enlarged. There is another enlargement at 

 the point where the lumbo-sacral plexus is given off. At this point, 

 superiorly, there is a longitudinal cavity called the sinus rhomboi- 

 dalis. This sinus contains a gelatinous substance. There is a pair 

 of nerves given off at each intervertebral foramen. Thus there are 

 as many pairs of spinal nerves as there are vertebral segments. The 

 inferior root is the motor root and carries the impulses from the 

 cord to the periphery. The superior root is the sensory branch 

 and carries the impulses from the periphery to the cord, and thence 

 the impulse is carried to the centers in the brain. The sensory 

 and the motor roots are of about equal size. The inferior have more 

 numerous filaments. The ganglion on the superior or sensory root 

 is relatively large. In the sacral region the sensory and the motor 

 branches pass through their own bony canal. 



White rami communicantes are given off at each intervertebral 

 foramen to the sympathetic system and gray rami are received from 

 the sympathetic ganglia. Thus there is established a direct commu- 

 nication between the sympathetic and the spinal system. There is a 

 ganglion on the superior root just outside the spinal cord. 



The ganglionic portion, or gray matter, is arranged in the center 

 of the cord in two comma-shaped parts forming an X. The white 

 matter, or the material forming the fibers, is arranged around the 

 central ganglionic portion. 



The spinal cord may be divided into two lateral symmetrical 

 halves. There are two longitudinal fissures, one on the upper and 

 the other on the lower half. The upper called the superior median, 

 fissure is narrow but deep. The one on the inferior side, called the 

 inferior median, is usually more pronounced. The superior parts 

 of the gray matter are called the superior cornua, or horns; the 

 inferior parts the inferior cornua, or horns. The center of the cord 



