THE SPINAL NERVES. 73 



from the sections that, in the adult, at least one vertebra 

 has been fused with the skull, and through the portion of 

 the cranium thus formed the roots of the first spinal 

 emerge, the caudal pair (dorsal and ventral) through one 

 foramen and the cephalic pair through another. 



In conformity with the nomenclature of Fiirbringer 

 ('97), the cephalic pair of roots and the nerves issuing 

 therefrom will be designated by the letter b, the caudal 

 pair by c. The ganglia of the nerves b and c fuse to a cer- 

 tain extent, so that it is impossible to determine with 

 precision from which source some the sensory fibres of 

 the peripheral rami come. The motor roots of b and c do 

 not, however, mingle, so that, though the relations of the 

 numerous rami at their origins are very complicated, yet 

 it is possible to trace each with precision to its root. 



The ventral roots are much larger than the dorsal, and 

 both roots of b are larger than the corresponding roots of 

 <:, the dorsal root c being very minute. As in the case of 

 all of the spinal nerves, the dorsal root arises at the 

 extreme dorsal side of the spinal cord, the ventral leaves 

 at its extreme ventral side, the two roots emerging 

 through the foramen at the same transverse level nearer 

 the ventral than the dorsal side. Some of the fibres of the 

 motor root c are clearly seen to arise from the fasciculus 

 longitudinalis dorsalis (Fig. i6). Their ultimate source 

 is unknown This root has two kinds of fibres, about 

 half of the number being less densely myelinated so that 

 in Weigert preparations they stain a much lighter blue 

 than the others. They are as large as, or even larger than 

 the others which are of the usual character of motor 

 fibres. Their significance is unknown, as they could not 

 be traced far in either direction. 



These roots and their rami are indicated in detail in 



