REPTILES. 131 



lying behind them. It is therefore not indeed the accessory piece of the Sternum of Saurians, but 

 rather the shield-formed plate, which is to be regarded as equivalent to the manubrium sterni of 

 Mammals. It still might be considered a question whether the so-called episternal bone [inter-clavicle'] 

 of the Ornithorhyncus and Echidna, which, like the accessory otci'nal piece of many Scaly Reptiles, 

 possesses anteriorly two lateral, transversely directed processes connected with the clavicle is not 

 developed in the same way as this bony piece of the Saurians, and has a like morphological significance. 

 We may admit, with some probability, that the same is no accessory element of the sternum, but a 

 long piece corresponding to the 'manubrium sterni' of other Mammals, since its position is not partially 

 under the remaining portion of the Sternum, but completely anterior to it. 1 



"SAURIA LORICATA" (Crocodiles}. 

 T/ie clavicles absent, but the interclavide developed. 

 Example. Crocodilus acutus, Cuv. 



The figures given (Plate XI, figs. 7 9) of the Sternum of this species are from dissections 

 of a ripe embryo, which had still a large mass of yolk in its abdomen ; they are magnified two 

 and one third diameters. 



The Shoulder-girdle moiety of the Crocodile (fig. 7) approaches very near to that of the 

 typical Struthious Birds, with the exception of the true Strutfiio : it has no transverse cleft across 

 the glenoid cavity, and there are no " fenestrae." The supra-scapula (s. sc.), at present quite 

 soft, is shaped like the blade of a hatchet ; and, like that of the Chamseleon, is less, relatively, than 

 that of a Lacertian. The scapula (sc.) is a flattened but thick bar, ossified all round, and some- 

 what expanded above and below : at present, a large tract of cartilage intervenes between this 

 " shaft" and the coracoid. Behind, this mass of hyaline cartilage is scooped to form the glenoid 

 cavity ; in front it expands and forms a short hook, the rudiment of the pra3-coracoid (p. cr.) ; a 

 very small rudiment it is, not equal to that of the Rhea and Emeu (see Plate XVII, figs. 4 and 7, 

 p. cr.). Properly speaking, the concave open space forming the front margin of the coracoid, is 

 the coraco-pra3- coracoid notch. The coracoid shaft-bone (cr.) is equal to the scapula in strength, 

 but it is one-fifth shorter . its epicoracoid region (e. cr.) is quite soft in the ripe embryo ; the two 

 main bars meet at a very obtuse angle. There is one splint to this Shoulder-arch, the inter- 

 clavicle (i. cl.) ; it is long-lanceolate, moderately thick at its narrowest part, which is nearly two- 

 fifths of the entire length of the whole bone. As Rathke truly says, this piece is formed entirely 

 in fibrous tissue ; that it is moderately hard when first perceptible, and that it soon becomes 

 dense by fresh development of bone-cells in the surrounding blastema : it is totally unlike the true 

 Sternum, being merely a subcutaneous derm-bone. At first sight this bone looks so like the 

 prse-sternal " rostrum" of the Heron (Arded), that it might easily be mistaken for it : fig. 9 shows 

 it from above, and how that it fills the groove below, and emerges from the notch in front of the 



1 This last remark of Rathke is the only one from which I must differ, for the three clavicular 

 bones of the Monotremes agree in all respects with those of the Saurians, and my figures (Plate XVIII) 

 show that the anterior part of the manubrium does lie inside the straight bar of the T-shaped piece ; 

 of which more hereafter. 



