THE SHOULDER-GIRDLE IN FISHES. 37 



Ostracion. The whole of each moiety (fig. 4 C, sc. cr.) is, as far as its cartilaginous basis is 

 concerned, of a very peculiar form ; denuded of its periosteal layers, it would be in the form of 

 a Fan-palm leaf, with the blade bent forwards on the stalk. The broad blade has a nearly 

 straight anterior margin ; below, also, the base of the blade (sc. p. cr.) is nearly straight, and the 

 stalk of cartilage, which is extremely delicate at the top, is set on behind the middle. The pos- 

 terior margin is strongly crenate, being cut into four crescentic notches (" glenoid notches") for 

 four of the brachial rays. The upper notch is the largest, the lowest next in size, and the upper 

 but one the smallest ; this coincides with the different dimensions of the proximal ends of the 

 brachials. There is no " scapular fenestra/' nor, indeed, scapular ossification ; but this region, 

 save where it is trespassed upon from below by the prse-coracoid (p. cr.) is entirely unossified, and 

 a soft tract of hyaline cartilage forms a headland in front of and behind the prae-coracoid. This 

 latter element (p. cr.) is fan-shaped ; it is flat in front, convex behind, and hollow in the middle, 

 that is, as it is seen from the outside ; the ossification is very much arrested, and but few of the 

 cartilage-cells are affected by the inner and outer " ectosteal " laminae. This specimen is either of a 

 small kind, or is the young of a larger one ; in either case the ossification would be less intense 

 than in a large specimen. The coracoid (cr.) has been very nearly segmented from the prse- 

 coracoid, only a slender rod of cells connecting the two regions. This delicate style of hyaline 

 cartilage thickens gradually in its lower parts, it is invested with a much stronger ectosteal sheath 

 than the prae-coracoid, and from the long styloid sheath wings project, toth fore and aft ; these 

 turn inwards, and form but little more than a right angle with each other. The bony matter of 

 the two regions is continuous where the " stalk " joins the " leaf," but nowhere else ; for the 

 " wings " of the stalk-like coracoid are entirely unconnected with the prae-coracoid ; a clear chink 

 can be seen both in front and behind (fig. 4 C, p. cr., cr.) There now arises a curious and, to 

 me, an unexpected difficulty ; for the periosteal wings which grow out from the rod-like coracoid 

 take the place of the "inter-clavicle " of the Ostracion (fig. 4 A, i. cl.). If my descent upon 

 this type had been made from the common Fishes I should have suspected nothing beyond what 

 is apparent ; but fresh from the Siluroids, the Lophobranchii, and the Ostracion ; and aware of 

 the atypical characters to be seen in Gasterosteus, soon to be described, I am prepared to believe 

 that there is more in the coracoid of the Tetrodon than meets the eye. The coracoid proper is 

 aborted by the large aponeurotic "inter-clavicle "in Clarias, Ostracion, and Gasterosteus; but in 

 Cottus bubalis (Plate II, fig. 12, p. i. cl.) the principal inter-clavicle lies close on the inside of the 

 coracoid, but quite free from it. Then we have seen its presence and its independent condition in 

 Syngnatltus (Woodcut, fig. 3 A, p. i. cl.), and, therefore, it is quite possible that there may have 

 been a distinct inter-clavicle in an earlier stage of this Fish the Tetrodon. This view is strength- 

 ened by the fact that these two elements are very apt to coalesce. On the other hand, any one 

 familiar with the structure and development of the endo-skeleton of the Teleostei knows how 

 apt the ectosteal sheaths of cartilaginous rods are to shoot out into Jarge wings ; a beautiful 

 instance of this is seen in the interspinous rays, especially of such a Fish as the Dory {Zeus}. 

 Thus there seems to be no absolute necessity to suppose that the double ectosteal laminae of the 

 prse-coracoid and coracoid were ever distinct in Tetrodon; they are in several Families of the 

 Malacopteri ; but the Tetrodon conforms rather to the Acanthopterous type. Undoubtedly, 

 the isthmus between the pra-coracoid and the coracoid was very much wider at an early period 

 than in this stage, which I am now describing, so that the first bony investment of the cartilaginous 

 plate would commence at the isthmus itself, and then, growing like a bent and flattened hour- 



