206 bulletin: museum of comparative zoology. 



the ophthalmic branch of the fifth nerve. Their origin from a cerebro- 

 spinal ganglion, their migration, their final incorporation into a ganglion 

 whence proceed motor peripheral fibres, are all strong indications of the 

 sympathetic nature of these cells. Yet, as His ('88 a ) has observed, errant 

 cerebro-spinal cells, which may remain eerebro-spinal in character 

 throughout life, cannot with certainty be distinguished in the embryo 

 from cells destined to become sympathetic. We must apply in addi- 

 tion the tests of histology after the cells have reached their adult 

 development. 



The greater part of the cells of the ciliary ganglion do not originate, 

 like those to which reference has just been made, from a cerebro-spinal 

 ganglion. It has been shown that a large proportion of the ciliary cells 

 become gradually differentiated in situ in the third nerve. The evi- 

 dence in favor of regarding these as migrant medullary elements has 

 been given. These ganglion cells, therefore, resemble in their develop- 

 ment neither cerebro-spinal cells, which stand in direct genetic relation 

 to the neural crest, nor sympathetic cells, the derivation of which from 

 cerebro-spinal ganglia can scarcely be questioned since the researches 

 of Onodi ('86), His, Jun. ('91), and others. 



The histological conditions which obtain in the ciliary ganglion of the 

 adult fowl bear out well the idea of its double nature. The occurrence 

 in the minglion of two regions, which were described in Part I of this 

 paper, is readily explained on developmental grounds. The smaller, 

 dorsal portion of the ganglion, whose small cells, slightly medullated 

 neuraxons and pericellular fibrils give evidence of its sympathetic char- 

 acter, lies on the side next the ophthalmic branch of the trigeminus, 

 and receives from that nerve the communicating ramus which so clearly 

 resembles a ramus communicans of the thoracic region. It is true, how- 

 ever, that the neuraxons given off peripherally lack the abundant medul- 

 lation characteristic of the post-ganglionic sympathetic neuraxons of the 

 thoracic region. If we consider that this part of the ganglion has origi- 

 nated from those cells which, in the embryo, migrated into it from the 

 Gasserian ganglion, it then may be said to conform to the sympathetic 

 type in its manner of development, as well as in nearly all its adult 

 histological details. One evidence of the sympathetic nature of this 

 region of the ciliary ganglion has not been adduced. The multipolarity 

 of its cells still remains a matter of assumption. Holtzmann ('96), it is 

 true, found both large and small cells in the ciliary ganglion of birds. 

 While the large cells are shown to be bipolar with large, medullated 

 processes, a typical small cell is figured with a single, slender, apparently 



