SCHULTE AND TILNEY, AEURAXIS IX THE DOMESTIC CAT 333 



region before closure occurs. Coincidently the medullary plate narrows 

 markedly so that it is probable that the primitive region of transition is 

 thinned out and added to the somatic ectoderm. When closure is effected 

 the ectoderm is closely applied to the concave dorsum of the neural tube 

 and is continuous from side to side, without median attachment to the 

 neuraxis, and with no intervening cells ( Plate XLI ) . We would empha- 

 size these facts, for they patently exclude the interpretation of the gang- 

 lionic crest of the trunk as an element intermediate between the general 

 ectoderm and neural tube, and primitively independent of the latter. In 

 this point our observations are in accord with the sections of the cat fig- 

 ured by Fleischmann* and of the human embryo by Felix" and agree with 

 Xeumayer's*' observations upon the trunk region of reptiles. It would 

 seem to follow, therefore, that the ganglionic crest of the cat is a deriva- 

 tive of the neural tube, and this view acquires an antecedent pro1)al)ility 

 from the occasional retention of afferent ganglion cells in the neuraxis of 

 "the adult, as in Amphioxus and Teleosts, and in the mesencephalic root 

 of the trigeminus of mammals. 



In the cat, the ganglionic crest is formed in the trunk Ijy a simple 

 delamination of the dorsal less regularly arranged cells at the summits 

 -of the neural folds. Shortly after closure a minute cleft appears on 

 each side and advances towards the midline, until the crests are attached 

 only by a narrow median strand. Again our results are concordant with 

 those of Neumayer for reptiles. 



Sometimes, and not always symmetrically, prior to closure, a faint 

 furrow appears on the ental surface of the neural fold close to the junc- 

 tion with the somatic ectoderm. This we have taken to indicate some 

 small degree of lateral movement of the cells at this point as though to 

 form an evagination. The process is abortive but suggests that in the 

 derivation of the ganglionic crest from the neural tube delamination 

 may have been substituted for evagination, and a solid anlage may have 

 replaced a hollow one, as elsewhere in the ontogeny of forms rich in cells. 



Farther cephalad the evagination becomes conspicuous. In the acous- 

 tico-facial region (Plates XXVI and XXX) there is a shallow obliriue 

 furrow unaccompanied- by evagination and the ganglion seems to agree 



* A. Pleisch.man-.\ : Embryologische Untersucbungen. Erstes Heft. Taf. II, figs. 4-G ; 

 Taf. Ill, figs. ?,-V2. Wiesbaden, 1889. 



■' W. Felix : "Die Entwickelung der Harn und Ceschlechtsorgane In Keibel and Mall," 

 Handbuch Entwiclvelungsgeschichte des Menschen. Figs. 522, 525, 528-530. 1911. 



" L. Neumayer : "Zur Morphologie des Central Nervensystems der Chelonier und Croco- 

 dilies." Aus Voeltzliow Reise in Ostafrilia in den .Tahren. 190.3-1005. Band IV. 191-t. 

 rber den Schluss der Seliiindaren MeduUarfurche und die Genese der Xeuralleiste. Ver- 

 handl. Anat. Ges. 22. 1913. "Histogenese und Morpliogenese des peripheren Nerven- 

 systems. der Spinalganglien und des Nervus sympatlieticus." Handbuch der Vergleich, 

 aind experiment. Entwiclcelungslelire der Wirbeltliiere. Hertwig.- 1900. 



