MOTOR NUCLEI IN PHYLOGENY 261 
DISCUSSION 
1. Intermedius complex 
Shortly after the publication of Brandis’ researches (l.c.), 
Firbringer (24, p. 504) commented on the probable existence of 
a correlation between the degree of differentiation of the dorsal 
XII nucleus in birds and that of their syringeal muscular appara- 
tus. Kappers subsequently has pointed out on numerous oc- 
casions that the central association of vagal and hypoglossal 
elements within the avian nucleus intermedius was highly sig- 
nificant in view of the fact that the musculature of the syrinx 
peculiar to birds is innervated by XII fibers, while that of the 
simple larynx in these forms derives its supply from the vagus 
nerve. The evidence collected by this author (see especially 
34), while not conclusive, is strongly in favor of considering the 
nucleus intermedius X as the motor laryngeal center, while 
doubt can no longer remain as to the innervation of the syrinx 
musculature largely if not exclusively from hypoglossal neurones 
of the intermedius complex. 
In the simply organized laryngeal apparatus in birds but 
two intrinsic muscles, an apertor and a sphincter, are present, 
while in the syrinx one or more pairs of proper vocal syringeal 
muscles, in addition to the paired extrinsic m. tracheo-clavicu- 
laris or m. sterno-trachealis, are present in the vast majority of 
birds. These facts for the most part accord well with the ob- 
servations noted above that in the majority of birds examined 
a definite X—XII intermedius complex is present. | 
There are, however, certain birds in which the syrinx is devoid 
of intrinsic musculature. All members of the family Ciconiidae 
lack true vocal syringeal muscles. They are absent also in a 
few members of the group Gallinae, as well as in Struthio, Casua- 
ris, and a number of other forms. It is probable that in these 
birds the absence of intrinsic syringeal musculature is to be 
considered due to the loss of muscular elements originally rep- 
resented rather than to the survival of a primitive character 
(cf. Newton and Gadow, 44; Beddard, 4). Such a conclusion 
would receive support from the fact that in both Ciconia and in 
