The Journal of 

 Comparative Neurology and Psychology 



Volume XV 1905 Number 3 



THE MORPHOLOGY OF THE VERTEBRATE HEAD 

 FROM THE VIEWPOINT OF THE FUNCTIONAL 

 DIVISIONS OF THE NERVOUS SYSTEM. ^ 



By J. B. Johnston. 



With Plates I to IV. 



TABLE OF CONTENTS. 



/. Introduction. 176 



a. Nature of the unsettled problems ..... 176 



b. Nerve components . . . . . . . -177 



c. Functional divisions of the nervous system . . . 180 



d. Bearing upon the subject of head morphology . . .182 

 2. Number and relations of mesodermic somites . . . . .184 

 J. Branchial apparatus and lateral musculature . . . .188 



4 . Segmentation of the central nen'ous system . . . . .191 



5. Typical sense organs of vertebrates . . . ■ ■ .194 



6. The anterior end of the head . . . . . . .197 



7. The segment containing N. III. Segment^ ..... 204 



8. Segment 6 2o7 



9. The absence of nerve roots from one or more hind brain segments and 



the determination of the neuromeres concerned . . . 211 



10. Segment 7. The acustico-lateral system . . . . .215 



11. Segments 8 and follozving . . , . . . . .2^3 



12. The occipital region and the posterior limit of the head. The constitu- 



tion of the vagus. Shifting of organs . . . . .224 



/J. The morphology of the visual organs ...... 233 



14. The nerves of Piatt, Locy and Pinkus ..... 244 



/J. Morphology of the olfactory organ. Functional and morphological 



relations to the gustatory system ...... 245 



16. The first four head segments ....... 249 



a. Segment 4 ......... • 249 



b. Segment 3 ......... • 250 



c. Segment 2 ......... • 250 



d. Segment i Prostomium ....... 252 



ly. The dorsal commisstires of the brain ...... 253 



1 Studies from the Zoological Laboratory of West Virginia University, No. 9. 



