CROCODILIA. 101 



coccygeal vertebrae demonstrate in the young animal ; the lumbar pleurapophyses 

 being manifested at the same period as cartilaginous appendages to the ends of the 

 long diapophyses. 



The scapulo-coracoid arch, both elements (51, 52) of which retain the form of strong 

 and thick vertebral and sternal ribs in the crocodile, is applied in the skeleton of that 

 animal over the anterior thoracic htemal arches. Viewed as a more robust haemal arch, 

 it is obviously out of place in reference to the rest of its vertebral segment. If we 

 seek to determine that segment by the mode in which we restore to their centrums 

 the less displaced neural arches of the antecedent vertebrae of the cranium or in the 

 sacrum of the bird,* we proceed to examine the vertebras before and behind the dis- 

 placed ai'ch, with the view to discover the one which needs it, in order to be made 

 typically complete. Finding no centrum and neural arch without its pleurapophyses 

 from the scapula to the pelvis, we give up our search in that direction ; and in the 

 opposite direction we find no vertebra without its ribs until we reach the occiput : 

 there we have centrum and neural arch, with coalesced parapophyses — the elements 

 answering to those included in the arch N i, fig. 13 — but without the arch H i; which 

 arch can only be supplied, without destroying the typical completeness of antecedent 

 cranial segments, by a restoration of the bones 50 — 52, to the place which they 

 naturally occupy in the skeleton of the fish. And since anatomists are generally 

 agreed to regard the bones 50 — 52 in the crocodile (fig. 13) as specially homologous 

 with those so numbered in the fish,t we must conclude that they are likewise homo- 

 logous in a higher sense ; that in the fish, the scapulo-coracoid arch is in its natural 

 or typical position, whereas in the crocodile it has been displaced for a special purpose. 

 Thus, agreeably with a general principle, we perceive that, as the lower vertebrate 

 animal illustrates the closer adhesion to the archetype by the natural articulation of the 

 scapulo-coracoid arch to the occiput, so the higher vertebrate manifests the superior 

 influence of the antagonising power of adaptive modification by the removal of that arch 

 from its proper segment. 



The anthropotomist, by his mode of counting and defining the dorsal vertebrae and 

 ribs, admits, unconsciously perhaps, the important principle in general homology 

 which is here exemplified, and which, pursued to its legitimate consequences and 

 further applied, demonstrates that the scapula is the modified rib of that centrum and 

 neural arch which he calls the ' occipital bone,' and that the change of place which 

 chiefly masks that relation (for a very elementary acquaintance with comparative 

 anatomy shows how little mere form and proportion afi"ect the homological characters 

 of bones) differs only in extent and not in kind from the modification which makes a 

 minor amount of comparative observation requisite, in order to determine the relation 

 of the shifted dorsal rib to its proper centrum in the human skeleton. 



* See 'On the Archetype and Homologies of the Vertebrate Skeleton,' p. 11", p. 159. 

 t Op. cit., fig. 5, p. 17. 



P 



