18 SHOULDER-GIRDLE AND BREAST-BONE. 



that cover the Shoulder-girdle. A fine skeleton of this Fish is to be seen (amongst Hyrtl's prepa- 

 rations) in the Hunterian Museum, and in it the relations of the so-called supra-scapula are well 

 shown. The temporo-parietal region is one mass of ganoid bone ; behind this helmet there are 

 two oblong bones, which become narrow where they meet at the mid-line ; these cover the supra- 

 occipital region. Below, and a little behind each of these, is a squarish, thick, ganoid supra-temporal ; 

 and behind this is the thick external part of the " post-temporal," the subcutaneous part of which 

 is triangular, and passes upwards and forwards to articulate with the inner lamina of the supra- 

 occipital derm-lone. The lower ganoid part of the bone overlaps and articulates with the super- 

 clavicle ; this is a lunate bone ; it is subcutaneous, and its pointed lower end overlies the great 

 falcate clavicle ; this latter bone has no inter-clavicular bone between it and its fellow of the 

 opposite side. Inside these, at their junction, the anterior edge of a flat, subcutaneous post- 

 clavicle passes ; this bone is the counterpart of the middle bone of the three described in the 

 Polypterus. The coraco-scapular cartilage inside the clavicle is soft, as in Calamoichlhys, and the 

 seven bony rays seem, in the dry preparation, to be obliquely attached to a cartilaginous pra> 

 brachial. I cannot satisfy myself, however, on this point. 



PISCES GANOIDEI (B., Fossil forms) . 

 Example 1. Glyptolamus. 



As a thorough understanding of the nature of the skeleton in the Ganoids is vital, not only 

 to the present inquiry, but also to any investigations concerning the morphology of the skeleton 

 generally, I shall depart from my rule of studying only recent forms, and give some account of 

 the extinct types of this group of Fishes. 



I shall refer the reader to the woodcuts in Professor Huxley's memoir (quoted above), so that, 

 by comparison of these figures one with another, with those of recent related types, with my 

 figures of the parts in the Sturgeon, and in the Siluroid Callichthys (Plate I, figs. 9 13), 

 and also with the skeletons of the recent Ganoids in the Hunterian Museum, a clear view of the 

 structure and relations of these parts may be obtained. 



Moreover, as I have to show, not only the structure of the outer and inner (or essential) parts 

 of the Shoulder-girdle, but also the relations that this arch has, fore-and-aft, to the rest of the 

 skeleton, I shall be under the necessity of giving some account of parts that are not actually 

 "in the bond." 



The Ganoids generally may, in a rough way, be said to lie between the Sturgeon and the 

 Polypterus, and it is of the utmost importance that the morphologist should have clear ideas 

 respecting the structure of these diverse recent types of this Order. The degree of ossification 

 of the en do-skeleton in the fossil genera ranged between these two extremes ; but throughout 

 there was evidently very little separation of the outer ganoid part of a derm-bone from the inner 

 or aponeurotic portion. As to the Skull and Shoulder-girdle, these parts are not in the least 

 ossified in the Sturgeon, whilst they have an unusual degree (for Fishes) of bony hardness in 

 the Polypterus ; intermediate conditions are common amongst the extinct types. In all Fishes 



