156 GENERAL ORNITHOLOGY. 
whence arise all the nerves of the body, excep those of the sympathetic nervous system). 
The lower ring is the hemal arch (Gr. aiwa, haima, blood), which similarly contains a section 
of the principal blood-vessels and viscera. Fig. 55 shows such a section, made across the 
thoracic or chest-region of the trunk. Here the upper ring (neural) is contracted, only sur- 
rounding the slender spinal cord, while the lower ring is expanded to enclose the heart and 
/ 4o5,400 
RFmo@2s 
o 2S S 
Oe Dion 
“mBeaeoe 
PBeyeos 
tS eye as 
= Th yee 
S 2k ee « 
Qe oO OD se om 
5BWeES ZS 
BESET SS 
NSB ee 
7B ZoaS 
72S 2 
POraas 
PA resi St (ey 
ae ®..0 
IZ ol = 
eS8taRgs 
A5baxz. 
)2:a = 
pee kastst 
we a's 
2ROsaaO 
oroekrer 
Br et teers 
EBsooNS = 
Se so - ON 
BOS Sela 
g tse 528 
UO 
eskairs 
Sosa) as rence 
=a Sane @ 
Doser £2 
Soauw peo 
mm AIP KOS 
Qraweegs 
ose = Chow 
HesTEes 
= & 
eels oge 
SaHRS SO 
se OW aot 
Le rst Oe at 
S2Eo08 SS 
Sa -So28s 
Som’ Foe 
2nOoow Ss. & 
SS) pan OO) ee 
Se Ros < 
2 Se et eee 
eS Oo ea 
eSRaTts¢ 
= omets 
Sin oe a 
R Sar 
RS SAS = 
ro Sey eee 
Be SO8st 
a 2 Ss 
Renee) Des 
SS SS) asin 
Suk alee 
woras es 
oOo". Se ES 
= ,co8eceg 
Se Sees 
SS So ae 
es eS eee 
ep OSS) teal et es 
= ee oa a 
P8600 8 on 
assasaes 
= = 2. 
ESE Os 
BR A 
A copier 
eS ec = 
ass Oo: 2 
nes 
Shy ep ea 
oR GY | om 
= o& © 
oOo..9ea 
mw = 6 i. Bs 
aad =e 
et bel 
th alo) 
wD Oe ean 
AoE scas 
Eos 
8 S83 ofo gs 
~ 7 ft Uae etie 
COAG, les gas 
4 EG aS oA 
»% BN EgEAE 
= ae aS 
! — SOS SS a 
i BRSQS.-0 
~ ” 
J ace ceioueies 
BEBBSS 
8 of 9 
lungs. Such a section, made in the region of the skull, would show the reverse; the upper 
ring greatly inflated to contain the brain, the lower contracted and otherwise greatly modified 
into bones of the jaws. Thus the trunk of a vertebrate is a double-barrelled tube ; one tube 
above for the nervous system, the other below for the viscera at large ; the partition between 
the two being a jointed chain of solid bones from one end of the body to the other. These 
solid bones are the centrums or bodies of vertebre, in the trunk; and in the head certain 
