20* 



LIFE, IN ITS HIGHER FORMS. 



running longitudinally through the animal. These pieces 

 are called vertebra. The best way to study a vertebra is to 

 take that of a Fish,— one of the joints from the backbone 

 of a Cod for example, since in this Class we find it most 

 simply and yet most perfectly developed. We thus per- 

 ceive that it is composed of several parts : — 1 . The central 

 cylinder; 2. the superior arch, formed by two sloping side 

 pieces, between which the spinal marrow passes ; 3. the 

 superior spinous process, projecting upward from the union 

 of these pieces ; i. the two lateral processes ; 5. the infe- 

 rior arch, formed as the superior is, protecting great blood- 

 vessels; 6. the inferior spinous process, pointing downward. 



A number of the vertebrae at the fore part of the column 

 are so far modified in shape and proportion of parts as to 

 be identified only by close study and comparison. They 

 constitute the skull, a capacious chamber of bone formed 

 to contain the brain, which is but the aggregation of seve- 

 ral pairs of ganglia greatly developed. 



In front of these bones there is placed another series, 

 arranged in pairs, constituting the face ; some of these are 

 excavated into cavities to protect the organs of sense, and 

 others form the jaws, &c. 



These may all be considered as integral parts of the 

 vertebral column ; but besides these, there are important 

 accessories yet to be noticed. First, there are a number 

 of slender bones, which are articulated to the transverse 

 processes of the vertebras, and arch outwards and down- 

 wards. They form two series : 1. The hyoid arches, 

 which spring from the skull : these are minute in the 

 human skeleton; but in some animals, especially in Fishes, 

 they are large and important, forming the great frame- 



