30 ARCHETYPE OF THE SKELETON. 



parapopliyses, p. Such vertebrae deviate but little from 

 the ideal type of the vertebra, under its less developed 

 condition, as in Fig. 6. The segments are commonly 

 simplified and made smaller as they approach the end of 

 the vertebral column or axis, one element or process after 

 another is removed, until the vertebra is reduced to its 

 centrum, as in the subjoined diagram (Fig. 7) of the arche- 

 type vertebrate skeleton. In this scheme, which gives a 

 side view of the series of segments or vertebr93, the nature 

 of the principal modifications to which they are subject 

 are indicated, at the two extremes of the series. 



As the four anterior divisions of the great trunk of the 

 nervous system are called, collectively, "brain," so the 

 four corresponding segments of the osseous system are 

 called " skull." The head, therefore, is not otherwise a 

 repetition of the trunk, than in so far as each segment of 

 the skull is a repetition or "homotype" of every other 

 segment of the body; each being subject to modifications 

 which may give it an individual character, without obli- 

 terating its typical features. So neither are the "arms" 

 and "legs" repeated in the head in any other sense than as 

 the cranial vertebrae may retain their "diverging append- 

 ages," 25, 37, 44, 53, a. The fore-limbs are actually 

 such appendages, 53, of the occipital vertebra, 1, 3, 2, 51, 

 52, 59, which appendages undergo modifications closely 

 analogous to those of the appendages of the pelvic seg- 

 ment, or "hind limbs," Qb. And inasmuch as in one 

 class the pelvic appendages, with their supporting haemal 

 arch, 63, lis^ are detached from the rest of their segment, 

 and subject to chaoges of position (Fig. 9), 63, 69 ; so also 

 in other classes the appendages of the occipital segment 

 are liable to be detached, with their sustaining haemal 

 arch, and to be transported to various distances from their 



