28 SHOULDER-GIRDLE AND BREAST-BONE. 



' Memoir on the Ganoids,' figs. 20, 21. The post-temporal plate (ibid., p. 30, fig. 20, 

 S. St.) has a large ganoid portion flush with the top of the flat skull, and articulated by suture 

 with the supra-temporal (S. T.) and the parietal (Pa. JEp.). Behind, it sends downwards a strong 

 peg of subcutaneous bone, which articulates with the anterior or supra-clavicular fork of the 

 clavicle. 



There are only two other dermal bones in relation with the true Shoulder-girdle ; for the 

 supra-clavicle ('Atlas,' plate 11, fig. lla) is not separate from the clavicle (a), but the inter- 

 clavicle (b) is nearly as large as the clavicle. These bones are very strong and fibrous, and only 

 part of the clavicle namely, the middle third below the pectoral fin, and the prickle in front of it 

 has any " ganoid" thickening. The junction of the dermal moieties below is very strong 

 indeed (see 'Atlas,' plate 11, fig. lib, and 'Mem. on Gan.,' p. 35, fig. 21), the sutural teeth 

 joining the inter-clavicle being especially large. As the true Shoulder- girdle is at first sight 

 almost indistinguishable in the adult, I shall describe its outlines first. The Woodcut (fig. 2 B) 

 shows these parts, full size, the view being the inside of the left moiety ; and it is seen that the 

 inter-clavicle (i. cl.) mounts up nearly to the division of the clavicle into a supra-clavicular and a 

 clavicular fork (s. cl., cl.). Here is seen at once a notable divergence from the structure of 

 CallicMhys ; and it may be remarked that a Memoir on the Osteology of the Siluroids would 

 be a great treasure, for these Pishes bridge over the space between the Ganoidei and the 

 Teleostei ; for if my first two instances, taken at haphazard, differ so intensely, it follows, of 

 course, that this great group would show a most instructive diversity. The clavicle is extremely 

 thick where it 'is deeply notched for the pectoral fin, having inside this part a deep crescentic 

 condyloid excavation for the serrated dermal ray (Woodcut, fig. 2 C, cl). Its middle third is 

 somewhat enamelled below the hinge. This part is shown to be divided by a groove from the 

 posterior third, in the hind view (fig. 2 C). It is well bent on itself, is concave within, and, gradually 

 widening below, runs into a large angular plate, which meets its fellow of the opposite side, and 

 is interlocked by rather small teeth. The inter-clavicle (i. cl.) is two-thirds the size of the clavicle, 

 and has much in common with it. On its hinder margin (fig. 2 B, i. cl.) it sends upwards a 

 prickle, then expands in an elegantly crescentic manner, narrowing again half an inch below the 

 fin, where it is considerably overlapped by the clavicle (fig. 2 C). Both these bones send 

 inwards an " aponeurotic" lamina ; and these laminae, joining together within and behind the 

 hinge, form a bridge over a deep rounded valley (fig. 2 B). There is a lesser valley behind the 

 lamina of the inter-clavicle and its posterior crescentic expansion, and in this valley lies the 

 coracoid (cr.). Above the hinge the two bones form another valley, deep and ditch-like. This 

 contains the upper part of the scapula (fig. 2 C, cl. sc.). The true Shoulder-girdle can only be 

 seen by using the pocket-lens ; then its different texture comes out ; but it is entirely anchylosed 

 to the great splints. In fig. 2 C, the scapula (sc.) is seen bridging over the bottom part of the 

 deep upper valley ; below this it is lost in the glenoid masses formed by it and by the clavicle 

 and inter-clavicle. A large bristle may be 'passed beneath the scapular bridge (fig. 2C, sc.). 

 The coracoid (cr.) may be seen in the postero-inferior valley, the bottom of which it fills, and in 

 it may be seen the coracoid notch converted into a fenestra by the inter-clavicle (cr. f., i. cl.) ; and 

 directly behind this another landmark, the coracoid foramen (fig. 2B, c. fm.), can be clearly seen: 

 so that, although the two great splints are persistently separate, yet the elements of the essential 

 Shoulder- girdle are not only entirely fused together, but. also with the enclosing splints. They 

 are very minute relatively, more so than in Polypterus, Amia, or Callichthys. There are only two 



