1 82 Journal of Comparative Neurology and Psychology. 



olfactoiius, area olfactoria, and tertiary tracts to coordinating cen- 

 ters in the diencephalon. 

 4. Sympathetic system, afferent portion. An outgrowth or offshoot from 

 splanchnic sensory ganglia which reaches a high specialization in 

 the vertebrate series. Consists of simple splanchnic sensory com- 

 ponent fibers and of ganglion cells which together with the efferent 

 portion form a somewhat complete or independent system. 



C. Somatic motor division. Consists of; 



ventral horn of the cord, nuclei of origin of Nn. XII, VI, IV, III, and 



nucleus of somatic motor fasciculus, 

 motor components in ventral roots supplying musculature derived from 



the somites. 



D. Splanchnic motor division. Consists of: 



1. Motor nuclei in lateral horn or intermediate zone of the cord and corre- 



sponding region of the medulla oblongata, 

 motor component in dorsal and ventral roots supplying musculature 

 derived from lateral mesoderm. 



2. Sympathetic system, efferent portion. Consists of simple splanchnic 



motor component fibers (?) and of ganglion cells and fibers con- 

 . cerned with glandular secretion, etc. 



In addition to the structures included in the above outHne 

 there are certain brain centers which with their fiber tracts 

 probably serve functions of coordination between the four pri- 

 mary divisions. It is not at present possible to define exactly 

 each of the functional divisions with its secondary tracts and 

 centers, or to understand fully the relations of the coordinating 

 structures even in the simplest vertebrate brains. Some con- 

 tribution upon this subject will be found in the following pages. 

 With one important exception (see Sec. i 5), however, sufficient 

 is already known for our present needs in discussing the homol- 

 ogy and segmental arrangement of the organs of the head. 



d. Bearing upon the subject of head morphology. 



The essence of the theory of functional divisions is this : 

 Each system of organs in the vertebrate body is connected by 

 definite fiber paths with certain nerve centers which direct and 

 coordinate the actions of those organs. Those peripheral and 

 central nervous structures which are related to a given set of 

 organs form a structurally distinct portion or division of the 

 nervous system extending through the length of the animal 

 and represented in successive segments by serially homologous 



