IOWA ACADEMY OP SCIENCE 
225 
The hypoglossal nerve is formed from branches of the first and second 
spinal nerves as Druener has stated. 
A comparative study of the morphogenesis of the sympathetic nervous 
system in birds and mammals reveals certain points of difference which 
evidently have phylogenetic significance. T'wo pairs of sympathetic 
trunks arise in the course of ontogeny in birds, while in mammals a sin- 
gle pair of sympathetic trunks is developed. In the early stages in mam- 
mals the prevertebral plexuses show their greatest development in the 
region of the suprarenals. In the early stages in birds, these plexuses 
show their greatest development in the sacral region. This character in 
birds is obviously correlated with the enormous development of the gang- 
lion of Remak which has no counterpart in mammals. The pulmonary 
plexuses in mammals arise from cells which migrate from the vagi along 
the walls of the bronchi. In birds cells wander from the slender branches 
of the vagi, lying along the walls of the oesophagus, directly into the 
anlagen of the pulmonary plexuses. In mammals the anlagen of the 
cardiac plexus arise in the angle between the aorta and the pulmonary 
artery. In birds the anlagen of the cardiac plexus arise in the atrial 
septum. These morphogenetic differences, doubtless, indicate that the 
sympathetic system has departed more widely from the original type in 
birds than in mammals. 
A study of the development of the sympathetic system in birds, as 
well as in mammals, warrants the conclusion that the nervous system 
is a unit of which the sympathetic system is a part homologous with the 
other functional divisions. The morphogenetic differences above pointed 
out in the development of the sympathetic system in birds and mammals 
obviously indicate specializatons in certain directions which have arisen 
in response to the peculiar conditions of the vegetative functions. 
SUMMARY. 
1. The primary sympathetic trunks in the chick arise during the 
fourth day of incubation, as a pair of cell-columns lying along the dorso- 
lateral surfaces of the aorta. The anlagen of the secondary sympathetic 
trunks arise about the beginning of the sixth day, as ganglionic enlarge" - 
ments on the median sides of the spinal nerves. These ganglionic en- 
argements are at first independent of each other, but become connected 
later by longitudinal commissures. The primary sympathetic * trunks 
reach their maximum development during the course of the sixth day 
and then give way to the secondary sympathetic trunks. These observa- 
tions do not differ essentially from those of His, Jr. 
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