THE SHOULDER-GIRDLE IN FISHES. 11 



vertebrate skeleton being thus traceable from the low, larval Ganoid Fish up to its continuation in 

 the human being. 



The supra-scapula of the Sturgeon (Plate I, figs. 6 and 7, s. sc.) is a thick trihedral plate of 

 soft cartilage ; it is expanded on its postero-external surface, against the overlying dermal plate, 

 and anteriorly grows forwards as a thick plate, somewhat convex within (fig. 7), and very concave 

 externally (fig. 6) ; its outline is that of a gooseberry-prickle, only inverted in position, and 

 blunt-pointed ; it is wholly segmented from the cartilage below. The lower surface is directed 

 backwards and downwards ; it is scooped into an oblong articular cavity, to receive the convex 

 head of the scapula, which fits into it as the humerus fits into the ulna in our own skeleton. 



The rest of the Shoulder-girdle moiety is not easy to describe (see figs. 6 8), for it contains 

 the coraco-scapular mass in a very primordial condition, both histologically and morphologically ; 

 it is like a mass of clay rough-modelled by the hands of the potter, but ready to become the 

 shoulder-blade of any kind of vertebrate creature whatever, as it shall " seem good to the potter 

 to make it." The general form may be described as an oblong trihedral bar ; bifurcate below, 

 and attenuating into a thin edge wherever it comes into contact with the dermal plates : its 

 surfaces are sinuous ; now convex ; and anon gently scooped. Above, it is narrowed, as it rises 

 in front into the highest and broadest part of the supra-scapular concavity ; it steadily broadens 

 downwards, and then becoming of great width and thickness has all the centre scooped away, a 

 large elegantly arched viaduct being formed, which looks from before backwards (Plate I, fig. 8, 

 sc. f.). The floor of this archway is deeply scooped, and through it, towards the outside, there is 

 an oval false (membranous) floor (fig. 6, c. s. f.). The inner wall of the archway is very thick 

 (fig. 8, p. sc.), the outer (fig. 8, sc.) is much thinner; the hinder, broad end of the floor is very 

 thick, and it has scooped in it five glenoid cups for the brachial series of cartilages : these depres- 

 sions lie in an arcuate line which turns downwards, behind (fig. 8, gl.) ; they are filled with fine 

 fibrous tissue, a species of joint existing here like what we shall see in the Cetacea. The con- 

 cavity of the floor of the archway becomes narrow in front and is then lost (fig. 7, upper part of 

 p. cr.) ; the cartilage here growing forwards and a little downwards ,as a distinct fork ; it is broad, 

 flat within (fig. 7, p. cr.), and expands externally and in front into a thin-edged disc, which is 

 slightly concave on the outside, where it adheres to the semi-transparent dermal bone (cl.), like 

 the " foot " of a Snail upon the window-pane. The main part does not alter its direction or 

 character (fig. 7, cr.), but ends abruptly below with a rather sharp edge (figs. 6 8, cr.) : it sends 

 upwards on its outer side a sharp lamina (e. cr.), which also, snail-like, applies itself to the 

 dermal bone outside of it. (i. cl.) This is the cartilage, the interpretation of which must be 

 made sure, or we shall lose the first fastenings of our argument. If a transverse line be drawn 

 through the middle of the " glenoid " facets, we shall see how far down the scapula extends : all 

 below is coracoid. But the thick inner wall of the great archway is m front of the thinner outer 

 wall ; the former is the pra-scapula and meso-scapula (p. sc.) in one half-cleft ray ; the latter is 

 the scapula proper (sc.), and answers to the hindermost bar in the ray (Plate I, fig. 2, sc.). The 

 floor in front of the glenoid facets is common to the scapula and coracoid, and the snail-footed 

 bar in which it terminates is the prse-coracoid (p. cr.) : the false, or membranous floor, is the 

 coraco-scapular fenestra (fig. 6, c. s. f.), and answers to the front fenestra in the Skate (fig. 2, 

 c. s. f.). The creeping foot at the lower part of the coracoid is the epicoracoid (e. cr.) -. it is but 

 little developed towards its fellow of the opposite side, and is thus very unlike the epicoracoid of 

 the Skate (Plate I, figs. 2 and 3, e. cr.). Opposite the bifurcation for the epicoracoid there is 



