668 



SKELETON. 



this dorso-ventral form (fig. 487.), and the re- (3, 3) encloses the haemal or visceral space 

 suit is fig. 488., having a pair of symmetri- (-J), and this arch, like the one above, has 



Fig. 487. 



k 



TJie dorso-ve.ntral archetypal quantity, taken from the 

 spinal series of the osseous fish. 



cal ribs (c c) terminated by symmetrical palms 

 or fins (9). The ventral space (c, c,fig. 488.) 

 is now an apartment enclosed by ribs, in 

 which are located the blood-circulating 

 organs, together with the viscera of self- 

 nutrition and reproduction. The dorsal space 

 (4) encloses the nervous axis. 



In fig. 487. the superior or neural arch (3,3) 

 encloses the neural space (4), and is sur- 

 mounted by the interspinous bones (2, 2), to 

 which is appended the symmetrical dorsal 

 palm (1, 1). The haemal or inferior arch 



Fig. 488. 



The dorso-ventral archetype, 



Showing how the ventral azygos ray is converted 

 into the opposite pair of ribs by a vertical bi- 

 cleavage through the median line. 



attached to it ventrad the interspinous os- 

 sicles (2, 2), to which is appended, in like 

 manner, the symmetrical ventral palm (1, 1). 

 All these elements of the dorso-ventral arche- 

 typal quantity (fig. 487.) are bicleayable by 

 the common median line (6, 6) passing per- 

 pendicularly through the centrum 5. If the 

 ventral laminae (3, 3) be sundered apart from 

 each other to a width equal to the circle 

 4*, 4*, then these laminae will enclose ventral 

 space like the symmetrical costae. The dor- 

 sal laminae (3, 3) are quantitatively equal to 

 the ventral laminae ; and it is possible for 

 the former to be sundered apart so as to 

 form a neural circular space equal to 4* 4* ; 

 but it never happens that this circular space 

 has occasion to be formed around' the neural 

 axis, for already the neural arch (4) is suffi- 

 ciently capacious for its contents, and there- 

 fore the space (4) formed between the dorsal 

 laminae (3, 3) is of dimensions, in all spinal 

 axes, equal to the spinal cord. 



But the symmetrical sides of the ventral 

 ray of the archetype (fig. 487.) do actually 

 widen apart from each other to a degree 



