168 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



B^raneck ('84) found the oculomotor, in an early stage of develop- 

 ment, arising from the ventral face of the mid-brain by a triangular 

 root crowded with cells possessing round nuclei, " et par touts leurs 

 caract^resserapprochent beaucoup des cellules meduUaires." Whether 

 this cellular accumulation at the root of the nerve is really ganglionic, 

 or whether its cells, like those distributed along the nerve, later form 

 the sheaths of the fibres, could not be determined. At the proximal 

 termination of the oculomotor occurs a little cellular mass, which the 

 author believes to represent the ciliary ganglion. At this stage no com- 

 municating branch exists between this or any other part of the third 

 nerve and the ophthalmic branch of the fifth. 



In later stages, numerous cells are to be seen distributed along the 

 whole nerve, those at the broad root being rounded and closely re- 

 sembling the medullary cells, while those more distally situated are 

 fusiform, with their long axes parallel to the nerve fibres. These dif- 

 ferences in shape among the cells of the oculomotor are more apparent 

 the older the embryo. The cells are more abundant in the proximal 

 than in the distal part of the nerve trunk. The approximately spherical 

 ciliary ganglion incloses round cells with distinct nuclei and fine gran- 

 ules. It is now connected by a slender ramus with the ophthalmic 

 division of the trigeminal nerve. From the anterior face of the ciliary 

 ganglion there runs cephalad, for an undetermined distance, a fine 

 bundle of fibres, which the author believes to represent the oph- 

 thalmic branch of the oculomotor described in sharks by Marshall ('81). 

 In old embryos, the ciliary ganwHon shows the relations to the third 

 nerve found in the adult : it is situated a little on one side of the nerve 

 trunk, to which it is attached by a very short and thick bundle of 

 nerve fibres. 



Nowhere in his account does B^raneok advance the theory that the 

 cells along the third nerve may have been derived through migration 

 from the neural tube, nor does he express an opinion as to the source of 

 the cells which differentiate in situ, in the oculomotor, into the cells of 

 the ciliary ganglion. 



The abducens appears somewhat later than the oculomotor, springing 

 as a slender nerve from the ventral face of the hind-brain. During its 

 development it presents but a single root, fibrillar in character, and des- 

 titute of cells, except for a few mesodermal elements which surround it 

 externally. The same conditions are found along the course of the 

 nerve trunk, the only cells connected with it being of mesodermal ori- 

 gin, arranged in a single layer about its periphery. 



