AMPHIBIANS. 83 



angle on the descending narrow bar ; this latter part does not cover all the cartilage behind, and 

 the former projects nearly as far forwards as the descending bar does downwards. The coracoid 

 (cr.) is now three times as large as the anterior bar, whereas it was once (fig. 1) only two thirds 

 the size ; it is much like that of certain Birds, having a thick swollen head, a roundish waist, and 

 a broad, expanded, pedate base. The prse-epicoracoid margin (e. cr.) is endosteally ossified, 

 and the submesial margins overlap in some degree. The coracoid fenestra (cr. f.) is of medium 

 size, is ovate, and its narrow end is now below instead of, as at first, above. The "omosternum" 

 (o. st.) has now a perfect ectosteal sheath a shaft-bone with no epiphyses even in this fine 

 old male ; but the posterior end is a narrow soft margin ; and the anterior, surmounting the 

 attenuated end of the delicate shaft, is a circular disc of cartilage. The sternum (st.) has a little 

 cartilage on the pra-sternal end of the single, hourglass-shaped flattened shaft ; and the xiphi- 

 sternal region (x. st.) is developed into a very elegant, symmetrical, transversely extended leaf, 

 which is notched at its retral angles, and at the mid-line behind ; its anterior part is ossified by 

 intercellular deposit, whilst a considerable margin is left in a soft state. When we come to the 

 Marsupials and to the Armadillo, we shall see very similar xiphisternal cartilages to this in the 

 Frog; the "omosternal moieties" have their "serial homologues" in the "Marsupial bones" 

 of the Marsupials and the Monotremes, these parts being segmented off from the " pubis," which 

 is the counterpart of the " pra-coracoid" in the Shoulder-girdle. 



Plate V, fig. 12, shows a section of the supra-scapula and scapula of the adult Frog 

 at their junction; and fig. 13, a section of the upper part of the supra-scapula: these 

 figures show the structure magnified twenty-five diameters. Fig. 13 shows the perichondrium 

 (pr.) passing over the hyaline cartilage (c.), with its clear intercellular substance, and its large 

 proliferating cells, full of young cells ; at the lower part the endosteal deposit (en. o.) is seen to 

 be an ossification of the intercellular substance, and not an cndo-pcrichondrial layer of bone like 

 that shown in fig. 14 (ec. o.). This section is exactly like a similar slice of the skeleton of a 

 Shark or Skate, save that the little bony masses are not so perfectly discrete. 



We see in fig. 12 that the cartilage-cells become very flat where the supra-scapula (s. sc.) 

 joins the scapula (sc.), and that the ectosteal and endosteal masses (ec. o., en. o.) have 

 united in the scapula to form solid bone : in the centre, however, certain sphaerical masses of 

 cartilage (c.) are seen unchanged ; in a higher Vertebrate these masses would, by proliferation, 

 have changed into marrow-cells, then into fat-cells, and then perhaps would have been altogether 

 absorbed. The projection of the endosteal masses into the base of the supra-scapula (fig. 12, 

 en. o.) looks very much like crystallization : undoubtedly it is a crystalline deposit, rendered 

 imperfect by the glutinous nature of the dissolving medium. 



I shall now refer to the views taken of these parts in the Batrachia by some of our great 

 anatomical pioneers : my friend Mr. Power has favoured me with the following translation ; I 

 shall insert my own nomenclature in brackets and in italics. 



I may here remark that the Sharks and Skates (Plagiostomi) shed the sauielight on the 

 Amphibia that the latter throw on the higher Vertebrata (the Sauropsida and Mammalia), which 

 .possess an amnion and an allantois in their embryonic condition, and which pass through their 

 metamorphic stages at a more and more rapid rate. The earliest metamorphic conditions of the 

 higher classes are miniatures seen for a moment ; those of the Amphibia are half-sized pictures, 



