96 DAVIDSON BLACK 



The dorsal position of the abducens nucleus is evidently the 

 result of the dominating influences of the dorsal tectobulbar 

 and vestibular fiber systems and its rostral migration in response 

 to tecto-bulbar impulses is limited by its important reflex con- 

 nections in the vestibular area (especially with Deiters' nucleus). 



The rostral migration of the trochlear nucleus in response to 

 tectobulbar stimulation in the absence of special reflex con- 

 nections in the bulb is only limited by the position of the oculo- 

 motor nucleus with which in Varanus and Chamaeleon it is in 

 close contact. It is of interest to note that the trochlear root 

 is also displaced rostrad in these forms as in birds. 



Finally, it would appear that the intrinsic elaboration of the 

 oculomotor nucleus evident in certain reptiles has also been 

 brought about under the influence of tectal impulses and ap- 

 parently in response to the special need for precise ocular fixation 

 due to the development in the retina of these forms of a point 

 of maximum visual acuity. 



LITERATURE CITED 



1 Adams, L. A. 1919 A memoir on the phylogeny of the jaw muscles in 



recent and fossil vertebrates. Annals N. Y. Acad. Sci., vol. 28, pp. 

 51-166. 



2 Baglioni, S. 1911 Zur vergleichenden Physiologie der Atembewegungen 



der Wirbeltiere. II. Tail, II. Reptilien. Ergeb. d. Physiol., Bd. 11, 

 S. 547-553. 



3 Bath, W. 1906 Die Geschmacksorgane der Vogel und Krokodile. Arch. f. 



Biontologie, Bd. 1, Heft 1, S. 5-47. 



4 Black, Davidson 1917 The motor nuclei of the cerebral nerves in phylo- 



geny. A study of the phenomena of neurobiotaxis. Part I. Cyclo- 

 stomi and Pisces. Jour. Comp. Neur., vol. 27, pp. 467-564. 



5 1917 Id. Part II. Amphibia. Jour. Comp. Neur., vol. 28, pp. 

 379-424. 



6 BouLENGER, G. A. 1889 Catalogue of Chelonians, British Museum. 



7 Bradley, Charnock O. 1903 The muscles of mastication and movement 



of the skull in Lacertilia. Zool. Jahrb., Abth. f. Anat. u. Ont., Bd. 18, 

 Hefte 4, S. 475-486. 



8 Bruner, H. L. 1907 On the cephalic veins and sinuses in reptiles with de- 



scription of a mechanism for raising the venous blood-pressure in the 

 head. Am. Jour. Anat., vol. 7, pp. 1-118. 



9 Cajal S. Ram6n 1911 Histologic du systeme nerveux de I'homme et de 



vertebres. T. 2. Trad, par Azoulay. Paris. 



