672 



SKELETON. 



to correspond with the bisected vertebral 

 centrum (6) of A. In c the laminae (4) and the 

 ribs (8) project in the same way from the 

 centrum (6). In c the transverse processes 

 (7, 7) project from the laminae (4), just in the 

 same relative position as the acromion pro- 

 cesses (7) project from the scapulae (4 of B). 

 In A there are no processes corresponding 

 with these ; but we should recollect that these 

 processes are merely apophyses, and not as 

 distinct elementary constituent parts of the 

 vertebral quantity. 



In A the symmetrical haemal spines or ossi- 

 cles (11) correspond to the bones of the fore- 

 arm (11 of B). In c the ribs (8) unite at the 

 sternal median line (10), and the ossicles (11) 

 are not existing. 



In A the ventral ray is terminated by the 

 palm 12, which is symmetrical; while in B 

 the scapulary members are terminated by the 

 palms 12, which are also symmetrical. These 

 palms are lost at the point 1 2 of c. 



When we compare A with B, we find that 

 all their parts correspond, except in this par- 

 ticular, viz. that A produces dorsad the bones 

 2 and the palms 1. In B these parts are lost. 

 When, again, we compare c with A, we find 

 that the parts 1 and 2, as well as the parts 

 11 and 12, are lost to c. It is this loss of 

 quantity which differences B and c from A. 



The existence of the parts 1, 2, 4 at the 

 dorsum, and of the parts 8, 10, 12 at the 

 ventrum of fig. A., renders this/g. symmetri- 

 cal and equal at the back and venter. The 

 obliteration of the parts 1 and 2 at the dor- 

 sum of B renders the figure unequal as to 

 back and venter. But the loss of the parts 



I and 2 from the dorsum of c, and the parts 



II and 12 from its venter, leaves this form 

 still similar as to back and venter, although 

 unequal to the dorso-ventral archetype (A). 

 This difference is merely quantitative. 



Notwithstanding this quantitative variety 

 between figs. A, B, and c, we still find them 

 symmetrically cleavable by the common me- 

 dian line, and this circumstance points to 

 their analogy. Fig. A. is a dorso-ventral limb ; 

 fig. B. is a ventral limb ; fig. c. is a ventral 

 costiform limb ; and it is a remarkable fact 

 that this latter quantitative form, though 

 usually performing those motions which are 

 required in the act of respiration, is, in some 

 species of animals (the ophidian and the 

 lizard), operative as a locomotive member. 



Fig. A. encloses neural and haemal space at 

 the points 5 and 9, and stands in spinal series 

 with all its fellows of that series. It is an 

 archetype compounded of the parts called 

 vertebra ; at the dorsum and venter'of which 

 stand the parts called the limbs. Fig. B. is a 

 proportional quantity of such another arche- 

 type as A ; and having suffered bicleavage 

 through its median line, it falls asunder on 

 either side of the animal, and encloses the 

 thorax between its opposite halves, at the 

 space 5, leaving the prehensile organs, con- 

 sisting of 8, if, 12, playing freely on either 

 side of the body. Fig. c. is a proportional 

 quantity, also of such another archetype as 



fig. A, and stands in spinal serial order with 

 this latter, enclosing neural and haemal space 

 at the points 5 and 9. The spinous ossicle 

 (3) which surmounts the laminae (4 of c), is 

 part of the quantity marked 2 in A, the 

 archetype. The spinous ossicle (3 of c) and 

 the epiphyseal nucleus (3 of B), which borders 

 the bases of the two scapulas, correspond. 



When fig. c. forms the sternum ( 10) by a 

 union of the ribs (8, 8), this sternal line in all 

 animals may be regarded as that median place 

 where the archetypal quantity (11 and 12) is 

 lost ; and in the same way, when c forms the 

 spinous union at the dorsum, surmounted by 

 the bilateral spinous ossicles (3), this spinous 

 point of the skeletal axis of all animals may 

 be said to be that place where the archetypal 

 quantity (1 and 2) has been subtracted. 



The mode in which the vertebriform sca- 

 pulae contract a connection with the costiform 

 clavicles and coracoid bones*, is similar to the 

 mode in which the vertebriform iliac bones 

 become joined to the costiform pubic, and 

 ischiadic bones, as a reference to fig. 491. will 

 prove. 



When the two iliac bones, to which are 

 appended the hind limbs, fall from vertebral 

 spinal series, bicleft on the animal's sides at 

 the lumbar region, they abut on either side 

 of that region of vertebral series, which hence 



Fig. 491. 



Showing the signification of the bones of the shoul- 

 der and hip ; that the clavicles, pubic and ischia- 

 dic bones refer to the ribs, while the scapulae and 

 iliac bones refer to the vertebrae. 



becomes the sacrum ; and the ilio-sacral sym- 

 physis is thus formed. 



In A (fig. 491.) the iliac bone (li, h) will be 



* I mean the bones called "coracoid" in birds 

 and reptiles, not the mammal coracoid processes, for 

 I have already named these latter to be the bicleft 

 centrum of the scapular vertebra. 



