In its embryonic condition this latter branch does not appear like a third branch of the fifth, equivalent to the seventh or the glosso-pharyngeal nerves, but rather resembles the branch of the seventh nerve which passes to the arch in front, which also is present in all the other cranial nerves.
Before concluding I will say one or two words as to my modes of preparation.
I have used picric and chromic acids, both applied in the usual way; but for the early stages I have found osmic acid by far the most useful reagent. I placed the object to be hardened, in osmic acid (half per cent.) for two hours and a half, and then for twenty four in absolute alcohol.
I then embedded and cut sections of it in the usual way, without staining further.
I found it advantageous to cut sections of these embryos immediately after hardening, since if kept for long in the absolute alcohol the osmic acid specimens are apt to become brittle.
Gegenbaur. _Anat. der Wirbelthiere_, III Heft, Leipzig, 1873.
A. Götte. _Archiv. für Micr. Anat._, Vol. X. 1873. "Der Keim der Forelleneies," _Archiv. für. Micr. Anat._, Vol. IX. 1873. "Untersuchung über die Entwicklung der Bombinator igneus," _Archiv. für Micr. Anat._, Vol. V. 1869. "Kurze Mittheilungen aus der Entwicklungsgeschichte der Unke," _Archiv. für Micr. Anat._, Vol. IX. 1873.
Kupffer. _Archiv. für Micr. Anat._, Vol. II. 1866, p. 473. Ibid. Vol. IV. 1868, p. 209.
Kowalevsky. "Entwicklungsgeschichte der Holothurien," _Mémoires de l'Acad. Impér. des Sciences de St Petersbourg_, vii ser. Vol. XI. 1867.
Kowalevsky, Owsjannikow, und Wagner. "Entwicklung der Störe," _Bulletin der K. Acad. St Petersbourg_, Vol. XIV. 1873.
Kowalevsky. "Embryologische Studien an Würmern und Arthropoden," _Mémoirs de l'Acad. Impér. des Sciences de St Petersbourg_, Vol. XVI. 1871.
E. Ray Lankester. _Annals and Mag. of Nat. History_, Vol. XI. 1873, p. 81.
W. Müller. "Ueber die Persistenz der Urniere bei Myxine Glutinosa," _Jenaische Zeitschrift_, Vol. VII. 1873.
Oellacher. _Zeitschrift für Wiss. Zoologie_, Vol. XXIII. 1873.
Owsjannikow. "Entwicklung der Coregonus," _Bul. der K. Akad. St Petersbourg_, Vol. XIX.
Romiti. _Archiv. für Micr. Anat._, Vol. IX. 1873.
_al._ Alimentary canal. _ao._ Dorsal aorta. _auv._ Auditory vesicle. _bd._ Formative cell probably derived from the yolk. _cav._ Cardinal vein. _ch._ Notochord. _ch´._ Thickening of hypoblast to form the notochord. _eb._ Line indicating the edge of the blastoderm. _ep._ Epiblast. _ep´._ Epidermis. _er._ Embryonic rim. _es._ Embryonic swelling. _gl._ Glosso-pharyngeal nerve. _h._ Head. _ht._ Heart. _hy._ Hypoblast. _ll._ Lower layer cells. _ly._ Line of separation between the blastoderm and the yolk. _m._ Mesoblast. _mc._ Medullary canal. _mg._ Medullary groove. _mp._ Muscle-plate. _mp´._ Early formed mass of muscles. _n._ Peculiar nuclei formed in the yolk. _n´._ Similar nuclei in the cells of the blastoderm. _na._ Cells which help to close in the alimentary canal, and which are derived from the yolk. _ny._ Network of lines present in the food-yolk. _ol._ Olfactory pit. _op._ Eye. _ov._ Oviduct. _pn._ Pineal gland. _pov._ Projection which becomes the ovary. _pp._ Pleuro-peritoneal cavity. _pp´._ Remains of pleuro-peritoneal cavity in the head. _prv._ Protovertebræ. _pwd._ Primary points of involution from the pleuro-peritoneal cavity by the coalescence of which the Wolffian duct is formed. _sg._ Segmentation cavity. _so._ Somatopleure. _sos._ Stalk connecting embryo with yolk-sac. _sp._ Splanchnopleure. _spn._ Spinal nerve. _sur._ Suprarenal body. _ts._ Caudal lobes. _v._ Blood-vessel. _vg._ Vagus nerve. V. Fifth nerve. VII. Seventh nerve. _vc_, 1, 2, 3, &c. 1st, 2nd and 3rd &c. visceral clefts. _vp._ Vertebral plates. _wd._ Wolffian duct. _x._ Peculiar body underlying the notochord derived from the hypoblast. _yk._ Yolk spherules.