MOTOR NUCLEI IN PHYLOGENY 543 
ventral musculature (hypopectoralis) but also to lateral trunk 
musculature (abductors and adductors of pectoral fin). In this 
animal as in other teleosts a ventral cell group is present in the 
rostral part and throughout the occipito-spinal nucleus. 
In Menidia a similar condition obtains only in addition to 
motor fibers to the ventral and lateral musculature the first 
precervical nerve sends out motor fibers to the dorsal trunk 
muscles of its own segment (Herrick, 1. c.). 
The relations obtaining in Ameiurus and Menidia may in a 
broad way be said to hold for all teleosts. At least it is evi- 
dent that the first precervical motor root in all teleosts becomes 
distributed to both ventral and lateral musculature, i.e., par- 
ticipates in the formation of both the so-called cervical plexus 
and the brachial plexus (Furbringer, |. c.). 
From this short review it becomes clear that the ventral cell 
group of the precervical somatic motor column first makes its 
appearance as a constituent of the most rostral portion of the 
nucleus in those forms in which the first motor root habitually 
participates in the formation of both cervical and brachial plex- 
uses. Conversely it is evident that among all forms in which the 
first precervical somatic motor rootlet is distributed entirely 
through the branches of the cervical plexus, a ventral cell group 
is lacking in that part of the nucleus from which the first motor 
root arises. 
It thus emerges that the ventral cell group of the motor 
occipito-spinal column of teleosts is apparently a nucleus of 
origin for motor roots distributed through the brachial plexus to 
dorsal or lateral derivatives of trunk musculature. Further, it 
would appear that the presence of this ventral cell group in the 
most rostral part of the precervical somatic motor nucleus in 
teleosts is due to the phylogenetic loss of the rostral, more 
specialized, dorsal cell group concerned in other forms in the 
innervation of epibranchial and pre-hyal hypobranchial spinal 
musculature, and is probably not the result of a forward migra- 
tion of ventral elements beneath a phylogenetically older dorsal 
cell group; for the evidence at our disposal points to the rostral 
migration of the constituent elements of the occipito-spinal 
nucleus of teleosts as a whole. 
