caepenteb: development of the oculomotor nerve. 207 



non-medullated process. The possibility that other fine processes might 

 have been torn off in the macerating and teasing method employed sug- 

 gests itself. Except for its unipolar condition this cell bears a close 

 resemblance to a sympathetic cell. 



The larger, ventral region of the ciliary ganglion bears little resem- 

 blance to a sympathetic ganglion. The cells in it a,re of greater size, 

 pericellular fibrils are not abundant, and its neuraxons are heavily me- 

 duUated. It seems safe to assume that from this portion of the gan- 

 glion were obtained by maceration the large bipolar cells with medullated 

 processes, the description of which has been given. While the neurons 

 in question resemble in medullation and size of ganglion cells those of 

 cerebro-spinal ganglia, some points of difference exist, the chief one be- 

 ing the bipolarity of the former and the unipolarity of the latter. As 

 has been stated, even when the ciliary-ganglion cells approach an unipo- 

 lar condition, the single stem does not divide at right angles to form the 

 typical T of a cerebro-spinal neuron. Inasmuch as we have assigned 

 to the dorsal or sympathetic portion of the ciliary ganglion the cells 

 which in the embrj'o migrate into it from the Gasserian ganglion, this 

 larger ventral region must have had its origin from those other and 

 more numerous cells which differentiate into nervous elements in situ 

 within the third nerve. These, as has been shown, appear to be mi- 

 grant cells from the ventral wall of the neural tube, a source from which 

 neither cerebro-spinal nor sympathetic ganglion cells are derived. 



It must be borne in mind, however, that the definition of an embryonic 

 sympathetic cell which is here implied, namely, a ganglion cell which 

 migrates out from a "stationai-y'' cerebro-spinal ganglion into a "va- 

 grant " ganglion (Gaskell), may be found by later researches to be in- 

 adequate. If later researches prove Harrison (:0l) to be right in his 

 supposition that sj'mpathetic ganglia receive contributions of migrant 

 motor cells from the neural tube via the ventral roots of spinal nerves, 

 then the two sources of the cells in the ciliary ganglion become identical 

 with the two sources of sympathetic cells. But the participation of me- 

 dullary elements in the formation of sympathetic ganglia has never been 

 actually observed. Investigators such as Onodi ('86), His, Jun., und 

 Eomberg ('90), and His, Jun. ('9l), who have made special studies of 

 the development of the sympathetic system, agree in deriving the cells en- 

 tirely from .spinal ganglia. Their conclusions have been generally accepted. 



The ciliary ganglion of the fowl is, then, to be considered as composed 

 of cells which fall into two categories, one being, as far as the evidence 

 goes, in all essential respects typically sympathetic, the other belong- 



