SKELETON. 



669 



according with the increasing bulk of the 

 viscera of the thorax and abdomen ; 

 and in order to allow space sufficient for 

 the reception of these organs, the ventral 

 ray (3, 2, 1) suffers a cleavage through its 

 whole length, as seen in Jig. 488., where the 

 original ventral ray (7, 8, 9) has widened into 

 the costal circle c, c. 



Now fig. 487., in its original azygos con- 

 dition, or in its bicleft symmetrical form in 

 Jig. 488., may be so metamorphosed and pro- 

 portioned as to produce every known form of 

 vertebra in the spinal axes of the four classes 

 of animals. The quantity of fig. 487., taken 

 as a whole or archetype, represents the larg- 

 est segment of all spinal axes, that, for ex- 

 ample, which we find standing in the spinal 

 axes of the Pleuronectidse. The obliteration 

 of several parts of the quantity (fig. 487.) will 

 successively represent in the remainders many 

 forms of vertebrae ; for if the dorsal palm 

 (1, 1) be subtracted from it, it will represent 

 ;my of the palmless dorsal rays of the osseous 

 fish ; and if the dorsal palm (1, 1), with the 

 interspinous ossicles (2, 2), be subtracted, 

 then the dorsal lamina? (3, 3), which enclose 

 the neural space (4), will represent any dorsal 

 ray of the spinal axis of the terrestrial animal. 

 When the dorsal and ventral palms (1, I), to- 

 gether with the dorsal and ventral interspi- 

 nous ossicles, are subtracted from the arche- 

 type (fig. 487.), then the quantity composed of 

 (5) the centrum and of (3, 3) the neural and 

 haemal arches equals that vertebra which we 

 find in the tail of cetaceans, viz. that vertebra 

 which possesses the chevron bones. The 

 chevron bones are fashioned of the inferior or 

 haemal laminae (3, 3), and when the neural or 

 the haemal arch produces the neural or the 

 haemal spinous process, this process is a part 

 of the interspinous ossicles left remaining, as 

 at g, g (fig. 488.) 



When the ventral ray (3, 2, 1) of the arche- 

 type (fig. 487.) widens to the costal arch c, c 

 in fig. 488., this arch is left standing at the 

 thorax of some animals, and even at the ven- 

 ter of others. As fig. 488. stands in its pre- 

 sent quantitative character, it may be found in 

 the abdomen of fishes still having the parts 

 1 and 2 attached and persisting, or obliterated 

 and lost to the original quantity, as the case 

 may require. At the dorsal aspect of the 

 spinal axes of all terrestrial animals it may be 

 understood that the parts 1 and 2 of fig. 488. 

 are lost or subtracted. 



It is the ventral ray, consisting of the parts 

 7, 8, 9 (fig. 488), which suffers median cleavage 

 and widens into the costal arches (c, c). As a 

 certain proof of this fact, I may remark, that 

 where the full ventral ray persists as at 

 7, 8, 9, there we never find the full costal 

 arches (c, c) existing; and where these latter 

 are existing, there we never find the ventral 

 ray. As the one becomes converted into 

 the other, it is hence impossible for the same 

 ens to exhibit both conditions of form at one 

 and the same time. 



When the ventral ray 7, 8, 9 (fig. 488.) has 

 widened into the costal arches, these arches 



may and do suffer a metamorphosis of quan- 

 tity to the same degree as when in their ori- 

 ginal azygos condition. Thus the ribs (c, c) 

 become symmetrically proportioned or oblite- 

 rated successively at the points /, e, d, by 

 imaginary lines radiating from the sternal 

 centre at 9. When these costal arches (c, c) 

 meet at the central point 9, then we name 

 the ribs sternal ; when they fall short of this 

 point 9, either at the point / or e, we name 

 these ribs asternal ; when they become ob- 

 literated as far back as the point d, then we 

 name them, as in the lumbar spine, the trans- 

 verse processes. 



As every law in nature is phaseal and gra- 

 duated, so i.s this the distinguishing character 

 of the law of formation. The ventral ray 

 (7, 8, 9), after undergoing a cleavage into 

 symmetrical halves, will present, in various 

 classes and species of animals, a phaseal gra- 

 dation in the process of widening, and assume 

 the form of the arc a, b, and c, successively, 

 according to necessity. 



In the caudex of the saurian or cetacean, 

 we find vertebrae producing at the same time 

 the neural arch and spine, the haemal arch 

 and spine, together with the costal process 

 (c, c), jutting laterally from the centrum (5) 

 as far as the point d ; when this is the case, 

 then the haemal arch and spine is fashioned 

 of that quantity of the costae which intervenes 

 between d and f, and which, being; severed 

 from c at the point d, is bent inwards towards 

 the median line 6, 7, thus assuming a second 

 time its azygos position. In some aquatic 

 mammalia (the porpoise, dolphin, ccc.) there 

 remains at the dorsal aspect some trace of the 

 dorsal form (], 2, 3, of fig. 488.). The ceta- 

 cean dorsal fin is thus explained. 



PROP. XLIII. The scapulary and pelvic 

 pairs of limbs are proportional quantities meta- 

 morphosed from the dorso-ventral archetypes. 

 The scapula disconnected from the clavicle is 

 the quantitative counterpart of the iliac bone 

 separated from the os pubis and ischium. 

 Having in a former place remarked upon the 

 structural homology which relates clavicles, 

 pubic bones, and ischiadic bones to ribs ; and 

 having also pointed out the homological rela- 

 tions between the scapulae and the iliac bones, 

 we shall in this place first consider the struc- 

 tural homology between these latter osseous 

 quantities and the vertebrae, and next the 

 homological relations between the fore and 

 hind limbs, the ribs, and the dorso-ventral 

 ra\ s. 



The dorsal vertebra, viewed from behind, 

 is represented in A (fig. 489.). u represents the 

 dorsal aspect of the two scapulae conjoined, 

 and c represents the two iliac bones placed 

 base to base. Is there a structural identity 

 apparent between these three figures ? and in 

 what points of character do they correspond; 1 

 To this question I answer in almost all 

 points ; for not only do these forms, viewed 

 in their entirety, correspond, but even their 

 mode of genesis is identical. 



The vertebra (A) is a symmetrical form, 

 consisting of opposite laminae (c, c), which 



