THE SYMPATHETIC NERVOUS SYSTEM IN MA.MMALS. 
175 
From this point the gangliation of the cord gradually proceeds until the condition 
found in the adult is produced. 
The truth of these observations has been tested by another method. Fig. 21 
(Plate 30) shows life-size drawings taken from dissections of Human embryos at 
various ages. In the dissections made, individual variations were found in the two 
sides of the same body—differences in the state of gangliation of the cord, as well 
in the arrangement as of the spinal communications. 
In an embryo in the third month (fig. 21, A.) the connecting branches from the spinal 
nerves were too fine to be seen with sufficient distinctness to warrant their being 
drawn. In the upper half of the thoracic region, the sympathetic cord formed a wavy 
band which swelled out above and below. Above, it joined the inferior cervical 
ganglion {I.G.), which was again connected by a narrower strip to the long, oval, 
superior cervical ganglion (S.G.), which occupied nearly the whole length of the neck. 
The vertebral [V.P.) and carotid plexuses {C.F.) were seen. The lower swelling of 
the dorsal band marked the origin of the first root of the great Splanchnic nerve 
{G.S 2 A.). In the lower dorsal region were two swellings, distinct, and connected to 
one another and the neighbouring parts of the cord, by short longitudinal commissures. 
Below these ganglia were two long oval masses separated by a slight constriction ; 
and below these, again, were two distinct ganglia joined by commissures. The last 
lay free and unattached (to spinal fibres), on the cartilage representing the second 
sacral vertebra. It is noteworthy that the diaphragm was complete in this embryo. 
In an embi-yo of the fourth month (fig. 21, B.) the cord again forms a uniform band 
in the tlioracic region, joined by the upper nine thoracic nerves. Angular projections 
(ganglia ?) are seen at the junctions of the spinal branches, and also where the roots 
of the Splanchnic nerves arise, especially in the case of the great Splanchnic {G.S 2 )l.). 
The thoracic band swells out above into the inferior cervical ganglion [LG.), which is 
joined by branches from the eighth cervical and first dorsal nerves. After giving off 
the vertebral plexus (F.P.) this forms a narrow commissure on which is a minute 
swelling, the middle cervical ganglion [M.G.), and finally broadens out into the 
superior cervical ganglion (S.G.), which ends above in the carotid plexus (C.P.). In 
the lower thoracic region two constrictions separate off a small mass, which is joined 
by branches from the tenth, eleventh, and twelfth thoracic nerves. Below the second 
constriction the cord forms a broad oval band, joined by the twelfth thoracic and all 
the lumbar nerves. Lastly, a sacral portion is constricted off, which consists of three 
fairly definite ganglia and a terminal filament, the ganglia being joined by the first 
three sacnd nerves. I was not able to trace the existence of a connecting loop 
between the lower ends of the two cords. 
In an embryo of the sixth month (fig. 21, D.) a very similar condition of things was 
found, so that it will be sufficient to note the differences from the last example. The 
inferior cervical ganglion (I.G.) was much larger: was joined by branches from the 
