142 



GENERAL ORNITHOLOGY. 



wh nee anse all the nerves of the body excepting those of the sympathetic nem.us system) 



cf th TnZ/l / / i^-- ''''^"' '"""' '^^^'^^' "'^^'^'^ ^^""^^^^ly contains a section 



of the pnncipal blood-vessels and viscera- Fig. 55 shows such a section, made across the 

 tUrac^c or chest-region of the trunk. Here the upper ring ,neural) is contracted, on ; sur 

 rounding the slender spinal cord, while the lower ring is expanded to enclose the heart and 



lungs. Such a section, made in the region of the skull, would show the reverse; the up,,cr 

 nng greatly inflated to contain the brain, the lower contracted and otherwise greatly mod Id 

 into bones of the jaws. Thus the trunk of a vertebrate is a double-barrelled tube ; <nie tube 



the tlfbl- ' "" "" T7.' ''' "''"■ '^''^ '•" ^^^ -^''^''''^ ■"' ^-g'^ ' the partition between 

 the two being a jointed chain of solid bones from one end of the body to the otl>er The.e 

 solid bones are the centrum, or hodies of vertebra, in tlie trunk; and in tlie hrad cerfu,i 



