NERVES OF THE DOGFISH 375 



THE FIRST THREE SPINAL NERVES 



The more anterior motor rootlets of the first spinal nerve ap- 

 pear a short distance posterior to the last rootlets of the occipital 

 nerve z, at a level slightly posterior to that of the posterior bor- 

 der of the roof of the cranium. The motor root thus formed 

 passes out at once through a foramen between the first vertebra 

 and the occipital condyle (fig. 43, sp.lrm.). On emerging, it 

 divides into a ventral and a dorsal ramus, the latter passing post- 

 eriorly and then anteriorly around the antero-lateral border of 

 the first spinal ganglion, apparently without receiving any sen- 

 sory elements from it, and gives off branches to the dorsal trunk 

 muscles. The ventral motor ramus, after sending off one or 

 more branches that run posteriorly in the ventral portion of the 

 dorsal trunk muscles, is joined by a sensory ramus from the first 

 spinal ganglion, the two forming a nerve which running poster- 

 iorly at the lateral border of the occipital condyle joins the two 

 occipital nerves as previously described (fig. 49). 



The sensory root of the first spinal nerve enters the dorsal 

 portion of the spinal cord somewhat posterior to the posterior 

 rootlets of the motor root. Its course from the spinal cord to 

 its foramen of exit through the first intercalary cartilage is pos- 

 teriorly directed, then anteriorly into the ganglion situated imme- 

 diately outside the foramen. From the extreme posterior end 

 of the ganglion a branch runs ventrolateral^ to join the ventral 

 motor ramus as described above. One or more (usually two) 

 sensory nerves connect with the anterior end of the ganglion 

 (fig. 49). 



The anterior rootlets of the second spinal nerve begin to emerge 

 as far anteriorly as the level of the sensory root of the first spinal 

 nerve. Numerous rootlets converge to form a root that passes 

 out at the level of the posterior rootlets through a foramen in 

 the first vertebra, dividing immediately on exit into a dorsal 

 and a ventral branch. In the number and arrangement of it? 

 parts the second spinal nerve is almost a duplication of the firs" 

 spinal. Its ventral ramus of motor and sensory composition 

 runs posteriorly at the lateral border of the first and second ver- 



