SHOULDER-GIRDLE OF FISHES. 7 



Class, however, the Hip-girdle so closely isomorphic of the Shoulder-girdle of the Skate in its 

 fixity above is seldom perfect below; the exception to this is that of the African Ostrich 

 (Struthio camelus)} 



The supra -scapulae (s. sc.) of the Thornback are separated from the scapulae (sc.) by a com- 

 plete transverse cleft, which results in a perfect joint-cavity, the highest type of segmentation. 

 Each supra-scapula (fig. 1, s. sc.) is irregularly four-sided, its upper edge straight, its anterior 

 concave, its posterior margin sigmoid ; whilst the scapular margin has an oblique convex outline, 

 the scapula (sc.) mounting upwards behind it. The supra-scapula is thick below, and thin 

 above (fig. 4), and by this its thin margin it is attached by strong fibrous tissue (there is no 

 joint-cavity here) to the jutting edge of the vertebral spine: it is gently concave above (fig- 4), 

 and as gently convex below. 



The scapula (sc,) can only be distinguished from the rest of the Shoulder-girdle by an eye ex- 

 perienced in these structures in the higher types of Vertebrata : once seen, however, in the light of 

 the nobler Classes, it reflects back a ray of the purest kind upon the morphology of the scapulas 

 of those creatures which at first illustrated it. Beyond the premature segmentation of the supra- 

 scapulae from the scapulas, there is nothing but abortive efforts at division, and the histological 

 state of these structures gives no waymark to the anatomist. The limb of one of the higher 

 Classes of Vertebrates may be compared to an espalier tree, with thick roots in the ground a 

 single stem, at first bifurcating, and then breaking into its ultimate branches ; but the limb of the 

 Skate is like such a tree, rich indeed in free, dividing branches, but starting from the very ground 

 itself with several " leaders." 



Fig. 2 shows three oval, smooth, synovial convexities (gl. 1, 2, 3), all lying in nearly the 

 same horizontal line ; and, whilst the outer ones are vertical, the inner is directed transversely ; 

 these are the three " glenoid " facets, and they articulate with the three " brachial " concavities. 2 

 (See Huxley and Hawkins' " Atlas," pi. xi, fig. 9.) 



The form of the scapula (fig. 2, sc.) is the reverse of what we have in Man, for the " neck " 

 is here of great width, and the " blade," where it joins the supra-scapula, is narrow ; this upper 

 part overlaps the supra-scapula behind, its concave edge going beyond the convex edge of the 

 upper plate. It widens gently in front, and the selvedge reaching from the supra-scapula to the 

 front glenoid facet (gl. 1) is scarcely convex : behind, however, its outline, which is elegantly concave 

 above, and then vertical below and behind, is directed at first more backwards than downwards. 



1 Here I may at once remark that the Hip-girdle is always, in the higher Classes, more complete 

 as to mere mass, and lower in type, morphologically, than the Shoulder-girdle ; so that whilst this part 

 in the Skate illustrates that in the Bird, in like manner the Shoulder-girdle of the Frog is no 

 inaccurate representation of the haunches of a Man. 



2 The mistake of making the " carpus" of the Fish articulate with the glenoid facets arose 

 from a misapprehension of the nature of the proximal bones of the fin. Cuvier called the clavicle of 

 the Osseous Fish " humerus," the scapula " radius," and the coracoid " ulna." Professor Owen called 

 the clavicle " coracoid/' the scapula " ulna," and the coracoid " radius." (See ' Owen's Lect. Comp. 

 Anat.,' vol. ii, pp. 117 126.) I have already challenged the whole of this nomenclature. (See 

 ' Zool. Proc., 1864, ' part iii, p. 341.) As the generalised condition of these fin-rays makes it difficult 

 to compare them with the limb-bones of the air-breathing Classes, I have adopted the term " brachial," 

 so as to leave the question of their special homologies open. 



