164 ANATOMY OF VERTEBRATES. 



Because the neural arch and corresponding muscular segment 

 have conditioned the beginning of the corresponding pair of 

 spinal nerves, it does not follow that the specially enlarged and 

 endowed appendage of such segment is arche typically an aggre- 

 gate of as many appendages as the nerve-pairs from which it has 

 attracted branches in the course of its growth and development. 

 But, on this assumption have rested the conclusions that the scapula 

 was an aggregate of all the cervical pleurapophyses, and that the 

 humcrus was the coalescence of the five diverging appendages 

 retaining their primitive and typical freedom in the five digits : 

 and,, by parity of reasoning, the scapula of the Skate should be 

 an aggregate of more than fifty pleurapophyses, &c. 



I assume that anatomists are agreed that the bone, vol. i. fig. 

 101, B, 51, is the homologue of 51, in fig. 101, A: that the scapula 

 of the Amphiuma answers to the bone so called in other Reptiles 

 and in Birds : and that the occipitally attached scapula of the 

 Lepidosiren is the homologue of the similarly named and con- 

 nected bone in other Fishes. But the long cylindrical rib-like 

 ' scapula ' of the Lepidosiren is one element, and the diverging 

 segmented appendage of the scapular arch manifests the like 

 essential unity. Now, the bifurcation of the distal segment of the 

 homologous diverging appendage in Amphiuma does not make 

 the unsplit part (fig. 101, B. 53) an aggregate of two appendages, 

 nor its scapula, ib. si, an aggregate of two ribs. And the same 

 may be predicated of five or any greater number of radiated 

 divisions of the terminal part of the scapular appendage. But 

 the pectoral fin of the Skate is the pectoral filament of the Mud- 

 fish, the fore-leg of the Quadruped, the wing of the Bird, the arm 

 and hand of Man : i. e. they are homologous parts though with 

 a supply of muscles, nerves, and vessels, according to their respec- 

 tive sizes, shapes, and uses. Say that the appendage in Lepidosiren, 

 fig. 101, A, 53-57, is a dermal development, and that the humcrus, 

 radius, &c. in its higher homologues, are skin-bones, and not 

 parts of the endo-skeleton : it does not follow that the scapular 

 arch, ib. 51, 52, is, also, part of the dermo-skeleton. What, then, 

 is it? This question I propounded, in 1846, l in reference to all 

 the parts of the vertebrate skeleton of which anatomists were at 

 one in respect to their special homology : it applies to the basi- 

 occipital (vol. i. fig. 77, i) and other elements of the occiput of the 

 Fish, as well as to the scapular arch therewith connected. What 

 is the basioccipital ? Anatomists are agreed that the ' basilar 

 process of the occipital bone' (Anthropotomy) is its homologue: in 



1 LXXIV, p. 276. 



