MORPHOLOGY OF EYE MUSCLE NERVES 57 



cle plates, the notochord and the aorta." The fact that some 

 nuclei found in the mesenchyma have a more deeply staining 

 quality certainly does not prove such an unqualified assertion. 

 That emigrated medullary elements enter into the sympathetic 

 is possible, but Kuntz has presented no facts that make this 

 inference seem more certain. 



So far as the evidence from sections of Squalus embryos goes, 

 it seems rather to favor the view that the sympathetic anlagen 

 receive their cellular elements largely if not exclusively from the 

 sensory ganglia, as inferred by investigators upon all classes of 

 vertebrates from Schenck and Birdsall to Held and Marcus. In 

 the first place there appears no reason to doubt the ventral 

 movement of the cells which enter into the formation of the 

 dorsal ganglia. The erltrance of cells into the sympathetic an- 

 lagen would involve only the continuation of this migration on 

 the part of some of these cells. The masses of cells which con- 

 stitute the anlagen of the sympathetic appear somewhat more 

 closely connected with the sensory bundle of the embryonic 

 nerve than with the motor bundle. Such relations appear in 

 frontal sections at the level of the ganglionic anlagen (fig. 30) . 



In Squalus, however, the separation between sensory and motor 

 bundles in the mixed spinal nerve, on the median side of which 

 the sympathetic anlagen first make their appearance, does not 

 appear as distinct as described by Held for other Selachii. In 

 such sections cells lie between the sensory and motor bundles, 

 and protoplasmic strands • connect the motor bundle with the 

 ganglia, so that the possibility that medullary elements enter 

 the ganglia from the motor root does not seem excluded. Con- 

 nection, on the other hand, by no means proves a migration. 

 Under the circumstances inferences appear most uncertain. 



But if one admit an analogy between the development of cra- 

 nial and spinal somatic motor nerves, there are facts connected 

 with the development of the oculomotor and the trochlear which 

 favor the inference of the predominantly ganglionic origin of 

 the sympathetic anlagen. For the first clusters of cells associ- 

 ated with the anlagen of these nerves are derived from the neural 

 crest. These cell clusters, in their relations and — in the case of 



