THE ORGANS OF SPECIAL SENSE. 603 



;The development of the different retinal layers can be studied in sections treated with the 

 above technic, but for the study of the development of the various nerve elements and their 

 relations recourse must be had to one or other of the Golgi methods (see "Practical Sug- 

 gestions," end of Chapter XVII). 



The Nose. 

 The nasal .pits can' be seen as depressions at the sides of the naso-frontal processes in 

 human embryos of 6 to 8 mm. (end of the first month), and'in other mammalian embryos of 

 corresponding stages. The further changes in the outer form can be followed in succeeding 

 stages. 



, • For changes in the interior, sections are of course necessary. A very instructive stage of 

 the development of the nasal septum, nasal chambers, conchas, and palate is shown in pig 

 embryos of 25 by 30 mm. (or human embryos of the same length; see Fig. 510). Fix the 

 embryo in Zenker's or Bouin's fluid, cut serial sections transverse to the long axes of the 

 jaws, stain with Weigert's haematoxylin and eosin, and mount in xylol-damar. Such sections 

 can also be used in studying the dental shelf (see Practical Suggestion's, p. 359). 



The Ear. 

 Owing to the fact that the ear (especially the labyrinth) is so complicated, it is practically 

 impossibk to study its development without the aid of reconstructions. The simple 

 auditory vesicle can be seen, however, in sections of pig embryos of 8 to 10 mm., lying close 

 to the side of the neural tube in the hind-brain region. In later stages, transverse serial 

 sections should be cut through this region and reconstructions made of the parts of the 

 labyrinth. The same technic can be used as given under "The Nose'' (see above). 



References for Further Study. 



The Eye. 



Gallenga: Entwickelung des Auges. Encyklopddie der Augenheilkunde, Lief. 6 and 7, 

 1902. 



Holden: An Outline of the Embryology of the Eye, New York, 1893. 



von Kollikee: Die Entwicklung und Bedeutung des Glaskorpers. Zeitschr. fur 

 wissensch. Zoolog., Bd. LXVI, 1904. 



Lange, O.: Einblicke in die embryonale Anatomie und Entwicklung des Menschen- 

 auges. 1908. 



Rabl, C. : Ueber den Bau und Entwickelung der Linse. Zeitschr. fur wissensch. Zool., 

 Bd. LXII and LXV, 1898; LXVII, 1899. 



Raymon y Cajal. : Nouvelles contributions a I'e"tude histologique de la ratine. Jour, de 

 VAnat. et de la Physiol, Vol. XXXII, 1896. 



Robinson. A.: On the Formation and Structure of the Optic Nerve and its Relation to 

 the Optic Stalk. Jour, of Anat. and Physiol., Vol. XXX, 1896. 



von Spee: Recherches sur 1'origine du corps vitre. Arch, de Biol., Vol. XIX, 1902. 



The Nose. 



Beard, J.: Morphological Studies. The Nose and Jacobson's Organ. Zool. Jahrbuch, 

 Bd. Ill, 1889. 



Disse, J.: Die erste Entwickelung der Riechnerven. Anat. Hefte, Bd. IX, 1897. 



His, W.: Beobachtungen zur Geschichte der Nasen- und Gaumenbildung beim 

 menschlichen Embryo. Abhandl. d. malh.-phys. Klasse Konig. Sachs. Gesellsch. d. 

 Wissensch., 1901. 



