26 



SHOULDER-GIRDLE AND BREAST-BONE. 



gl.3 



inner lamina is seen in fig. 11 ; its hinder convex aspect is seen in fig. 12 ; here it is seen to 

 resemble, very accurately, a semi-lunar aortal valve : part of this half-moon-shaped plate belongs 

 to the supra-clavicle. The extension downwards of the clavicle enables each bone to meet its fellow 

 at the mid-line ; but the suture is of short extent (fig. 13, cl.) Behind this descending part 

 there is a large semi-elliptic notch, which is converted into a foramen by the inter-clavicle : 

 through this space the " glenoid " bosses (gl.) of the coraco-scapular plate pass. 



The inter-clavicle (i. cl.) forms a large base to the clavicular triangle (fig. 9) ; it is articulated 

 to the clavicle by a finely toothed suture, which is broken at the great passage for the pectoral 

 fin. The lower margin of the ganoid plate of the clavicle is convex, the corresponding upper 

 edge of the inter-clavicle concave : there is a shallow fossa along this line, in which the pectoral 

 fin lies when at rest. Nearly the whole of the inter-clavicle is ganoid (see fig. 13, i. cl.) ; the 

 subcutaneous part is triangular, and with the corresponding part of the opposite side forms a 

 lozenge, the halves of which are united by a strongly toothed suture : more than two thirds of 

 the inner margins of these bones are free, and diverge more and more behind. Here, in this 

 Siluroid, we see very much of the Sturgeon, and a great unlikeness to the typical Teleostean ; 

 but the clavicles do meet below, as in the latter. 



There is still another plate which has relation to the Shoulder-girdle ; this is the " second 

 infero-lateral " or "post-clavicle" (fig. 9, p. cl.), the subcutaneous part of which is represented 

 by one, two, or three bones in the Teleostei proper. (See Plate I, fig. 14 ; and PI. II, figs. 

 6 and 8, p. cl.) 



If only the inner part of cl. and p. cl. in fig. 9 were developed, then the latter would at its 

 upper part pass in behind the former at an angle a few degrees below a right angle. (Compare 

 Plate I, figs. 9 and 14; and Plate II, figs. 6, 7, 8, and 12, cl. p. cl.) 



SHOULDER-PLATES OF SILUROIDS. 



A. CALLICHTHYS: left side; inner view. B, C. CLARIAS : left side; B inner, and C hinder view. 

 FIG. 2 A. FIG. 2 B. FIG. 2 C. 



(Magn. 4 diam.) (Nat. size.) (Nat. size.) 



p.cr. 



c.fm. 



i.cl 



s. cl. 



i. cl. 



