CRANIAL SYMPATHETIC GANGLIA IN THE PIG 73 



The following observations are based almost .exclusively on 

 embryos of the pig. As in my earlier investigations of the devel- 

 opment of the sympathetic nervous system, ^ the most satisfac- 

 tory preparations were obtained from embryos which were fixed 

 in chrom-aceto-formaldehyde, cut to a thickness of 10 ^ and 

 stained by the iron-hematoxylin method. This method was 

 employed almost exclusively in the present in\^estigation. Sagit- 

 tal, or parasagittal sections were found to be most serviceable 

 for the study of the cranial sympathetic ganglia and were used 

 almost exclusively. 



1 take pleasure in expressing my sense of obligation to Prof. 

 G. L. Houser for valuable suggestions during the progress of 

 this investigation. I desire also to express my indebtedness to 

 Prof. F. A. Stromsten for material assistance in technique. 



OBSERVATIONS 



Introductory 



The cranial sympathetic ganglia are genetically related to the 

 oculomotor and the trigeminal nerves. A study of the develop- 

 ment of the former, therefore, involves a study of the early 

 development of the latter. The relation of the cranial sympa- 

 thetic ganglia to the oculomotor and the several divisions of the 

 trigeminal nerves is illustrated in the accompanying figure (fig. 

 1) which is drawn semidiagrammatically from a wax reconstruc- 

 tion of the third and the fifth cranial nerves in an embryo of the 

 pig 27 mm. in length. 



Trigeminal nerve 



The trigeminal nerve arises from the wall of the anterior region 

 of the rhombencephalon by a relatively small motor root and a 

 larger sensory root upon which is located the semilunar ganglion. 

 The ophthalmic and the maxillary divisions of the trigeminal 

 nerve arise as fibrous outgrowths from the semilunar ganglion. 

 The motor root of the trigeminus takes part only in the for- 

 mation of the mandibular division. In embryos of the pig 5 to 



2 See bibliography. 



