76 SHOULDER-GIRDLE AND BREAST BONE. 



sides, this Sternum ends in two elegant xiphisternal auricles, separated by a notch of their own 

 width. This is my only example of a symmetrically ossified Sternum in the Amphibia ; but it is 

 a foreshadowing of what is constant in the Reptiles ; constant, but with the addition (as a rule) 

 of an intercalary piece in Birds, and not at all infrequent in the Mammals. 



Example 2. Calamites cyaneus, Fitzinger. 



Plate VII, fig. 6, shows the Shoulder-bones of this Australian type, magnified three 

 diameters ; it is drawn from the skeleton of an adult male. 



The supra-scapula (s. sc.) is much squarer in form than the last, and the anterior 

 margin is convex, whilst the posterior is concave, contrary to the rule ; and this change 

 affects the length of these margins also in some degree : but the anterior lobe of the outer 

 bone is largest, as usual, and the uncovered cartilage is partly calcified throughout most of 

 its extent. 



The scapula (sc.) has its prse-scapular fork (p. sc.) larger than the last ; the prse-coracoid 

 (p. cr.) is also longer, and its pedate base is more extended; the coracoid (cr.) is slenderer, the 

 overlapping epicoracoid (e. cr.) narrower, and the coracoid fenestra (cr. f.) twice as large, and 

 somewhat reniform. The omosternum is small, shark-tooth-shaped, and having an ectosteal 

 " crown," and soft, diverging " fangs " a remnant of the original dividing-line notching this 

 plate behind. In the true Sternum (st.) this division is very much greater ; and although these 

 two plates are not unlike, yet the true Sternum has no ectosteal sheath ; it is, however, affected 

 throughout by " endostosis." The prae-sternal margin is rounded, and this manubrial part is 

 only one third the length of the free, diverging " xiphisternal horns." Here we have an 

 anticipation of the long free xiphisternals of the Stellio Lizard ; of the Tinamou, Rails, &c., 

 among the Birds ; and of the Pangolins (Manis brevicauda, PJiolidotus Africanus), among the 

 Mammals. 



C 2. Sternum with an Ectosteal Sheath. 

 Example 1. Cystignathus pachypm, Wagler. 



Plate VII, figs. 2 and 3, shows the shoulder-plates of an adult male (from Bahia) magnified 

 three diameters. This is a truly elegant structure, and approaches very nearly to the highest 

 kind of Anouran development. 



The supra-scapula (s. sc.) is of the normal form, and the large ectosteal plate is hatchet- 

 shaped ; its anterior edge thick, and revealing, in the angle, a patch of unchanged cartilage, 

 besides the soft upper margin. This depends upon the development of an upper, independent, 

 endosteal plate, as in Bufo vulgaris, bearing the same relation to the supra-scapula itself 

 that the epiphyseal supra-scapula does to the scapula in the Mammal, and even in 

 the Reptile ; it is, essentially, a rudimentary, uppermost ray, thus making three supra-glenoidal 

 regions : in Anguis, as I shall soon show, the scapula itself is merely an epiphysis to the coracoid 

 shaft. 



The scapula (sc.) is a stout boot-shaped bone, with a prse-scapular fork (p. sc.) below ; the 



