136 GENERAL ORNITHOLOGY. 
whence arise all the nerves of the body, excepting those of the sympathetic nervous system). 
The lower ring is the hemal arch (Gr. aiya, 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 
whereof py is the pygostyle; s, scapula; 
; dv, dorsal vertebra, excepting the last one, 
see note 2, p. 138.) 
physes), whereof sr is sacral; w, one of the five uncinate processes or 
whereof the sixth floats; p, pelvic or sacral region of the spine, com- 
and urosacral vertebre; J, ilium; Js, ischium; P, pubis; a, acetabu- 
(For extent of dv, 
of an owl, Asio wilsonianus, life size; from nature by Dr. R. W. Shufeldt, U.S. A. 
caudal or coccygeal vertebr, 
, cervical ribs, or free pleurapophyses 
Fig. 56.— Axial skeleton, minus the skull, 
3 R, two of the six true ribs (pleurapo 
at, atlas; az, axis; cv, cervical vertebrx; c, c/ 
which joins the sacrum 
epipleura; cr, two of the six sternal ribs (hamapophyses), 
prehending one dorsal, and several lumbar, sacral proper, 
lum; in, ischio-iliac foramen; 0, obturator foramen; clv, 
ohs, os humero-scapulare; cl, clavicle; C, coracoid; S, sternum. 
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 vertebrae, in the trunk; and in the head certain 
