654- 



SKELETON. 



/ !\ \ 



osseous sternal median line produced for the 

 most part of set dimensions ; but when I 

 Fig. 480. extend my comparison through all individuals 



of that class, I find the sternum to be created 

 of variable length, and constituted of variable 

 numbers of elemental pieces. When, further, 

 I carry my observations through all indi- 

 viduals of the four classes, fishes, reptiles, 

 birds, and mammals, I find that the osseous 

 sternal median line has no limit short of the 

 space which the maxillae mark before, and the 

 pubic arches behind. Hence it is that I call 

 every sternal apparatus, which happens to be 

 created of lesser dimensions than this space, 

 as a specialty cut from the transcendent 

 line of sternal median uniformity, such as 

 Jig. 480. represents, with the piscean neck A B, 

 the mammal thorax c D, and the reptilian 

 venter and loins E F. Now, the hyoid appa- 

 ratus (a,b,c,d) occurs at the median line of the 

 cervix (A B, Jig. 480) where we know costal 

 quantity to be subtracted. The costo-sternal 

 apparatus (n,b,c,d) happens at the median 

 line of the thorax (c D), where we still view 

 costal quantity persisting. Let these two 

 facts be submitted to the focal light of com- 

 parison, and I doubt not but that reason 

 must draw the conclusion, that as the ventral 

 sternum (fc k) relates the pubic symphysis 

 (c* d) to the thoracic sternum (i, i), so 

 does the hyoid sternum as a cervical ster- 

 num (g, h) relate the maxillary symphysis 

 to the thoracic sternum (i, i). Hyoid ap- 

 paratus is, therefore, but a name by which 

 we designate the degree of metamorphosis to 

 which the original costo-sternal series of a 

 cervix has been subjected. It is this meta- 

 morphosis which has rendered the costo- 

 sternal quantities, proper to the cervical ver- 

 tebra?, into the vocal organs of one class of 

 animals, into the laryngeal organs of all ani- 

 mals, and into the branchial organs of the 

 fish (A B), in which latter class the character 

 of the original costo-sternal apparatus is least 

 modified ; for evidently the hyoid or branchial 

 apparatus (a, b, c, d) of the fish (A B) is consti- 

 tuted like the thoracic apparatus (, b, c, f/)of 

 other animals (c D), of a series of ribs joining 

 a sternal median line. 



The greater the degree of metamorphosis 

 which the archetype has undergone, the 

 greater is the obscurity of that structural 

 analogy existing between organs of the same 

 order in two or more animals. 



But though we are accustomed to limit the 

 name sternum as applicable alone to the osseous 

 part of the common and general median line 

 of the mammalian animal, and though we do 

 not usually recognise as a sternum in this 

 class that region of the median line which 

 presents in cartilaginous structure, as, for ex- 

 ample, at the neck and venter, still I maintain 

 that, so long as it is acknowledged that com- 

 parison is the only instrument by which we 

 can ever hope to ascertain the law of form- 

 An archetypal skeletal axis, constructed^/ ifiej^iscean at ; on j n the creation of special differences, we 



cervix, the Mammalian thorax, and the Reptilian 

 venter and caudex, 



Showing the original serial continuity of the ribs 

 and sternal median line. 



must interpret the linea alba as being the 

 continuation of the sternal line in the mammal 

 abdomen, and the cricoid, the thyroid, and 



