IOO PLATT. [Vol. V. 



ganglion. I believe, however, that the proper ganglion of the 

 thalamic nerve atrophies between the optic vesicle and the 

 brain, where a group of cells are long found which stain differ- 

 ently from the surrounding cells. The ciliary ganglion can 

 hardly be the proper ganglion of the trochlearis, since this 

 nerve has its own ganglion lying above the superior oblique 

 eye-muscle ; and if all of the original ganglion cells of the troch- 

 learis are not here represented, they are surely to be looked for 

 along the line of the original connection between this ganglion 

 and the Gasserian ; in other words, on the path of the ramus 

 ophthalmicus superficialis trigemini, and not on that of the ramus 

 ophthalmicus profundus. The latter never occupies the position 

 of that remnant of the neural crest which ventrally united the 

 rudiments of the trigeminal, trochlear, thalamic, and olfactory 

 nerves. I therefore consider the ramus ophthalmicus profundus 

 a commissural nerve, resembling that nerve which connects the 

 several vagus ganglia, and must leave the question to which of 

 the main divisions of the neural crest the ciliary ganglion pri- 

 marily belongs, quite unanswered. 



The fact that both the oculomotorius and the permanent 

 trochlearis are formed by the proliferation of ganglion cells 

 towards the brain makes it highly probable that these nerves 

 are both primarily sensory. At an early stage the ciliary gan- 

 glion is intimately connected with a thickening of the epithelium, 

 which, if sensory, as seems probable, would transmit to the 

 brain any impulses it received most directly by way of the 

 oculomotorius. It may also be remembered that the walls of 

 the premandibular cavity do not develop muscle cells for some 

 time after the first appearance of the oculomotorius, from which 

 it seems that the nerve is sensory prior to the acquisition of its 

 motor function. The connection of the ciliary ganglion with 

 the floor of the mid-brain by means of the oculomotorius, I 

 believe to be a secondary attachment, homologous to the sec- 

 ondary attachments of other ganglia to the brain. Van Wijhe 

 (No. 1 6) suggests that the optic nerve is morphologically ante- 

 rior to the olfactory. I think that he is right, and I sometimes 

 suspect that the oculomotorius is morphologically anterior to the 

 opticus. 



The development of oculomotorius and trochlearis in Acanthias 

 tends to show that Balfour (No. 2) was right in considering the 



