THE SPINAL NERVES. 69 



Stimuli arising- in the contracting segment and transmitted 

 to the spinal cord through the r. communicans might be 

 of use in regulating the motor impulses to be transmitted 

 to the next following segment through the r. spinosus. 

 The anastomosis with the r. lateralis accessorius is in 

 every segment examined a very broad one, the entire 

 sensory component of the dorsal spinal ramus passing 

 bodily into the r. accessorius. See the latter nerve for 

 further mention. 



The relations of visceral fibres to the spinal nerves have 

 not been investigated, as my methods are not adapted for 

 that research. 



II. — The Third Spinal Nerve. 



The origin of the third spinal nerve resembles that of 

 the fourth except that the roots are larger; they emerge 

 in the same way by separate foramina in the second free 

 vertebra, and exhibit the same difference in the calibre of 

 the fibres. The coarse ventral fibres, as before, can be 

 traced through the ganglion. Of the dorsal rami, the 

 r. spinosus^ r. sp. j (wholly motor), and the r. communi- 

 cans, r. com. J (wholly sensory), are as in the last case; so 

 also the r. inediiis, r. vi. j, save that the number of its 

 sensory fibres is smaller. 



The ventral ramus {r. v. j) is large, the sensory portion 

 being more than three times the size of the motor, which 

 is of about the average size for a spinal nerve. It gives 

 off immediately a minute twig for the dorsal musculature 

 (not shown on the plot), and then runs under the dorsal 

 musculature to the lateral edge of the latter, where it 

 breaks up into three branches. Two of these, which are 

 composed of fine fibres, run caudad and laterad, the first 

 running up over the depressor of the pectoral fin and 



