BIRDS. 187 



of the coracoid is strongly incurved, and the meso-coracoid (op. cit., fig. 1, cr.) runs up to the 

 acromion, and is present, as a distinct ridge, down the inside of the bone, as in Psophia, but not 

 to the same degree. The coracoids do not meet on the front of this, the most extraordinary 

 ornithic Sternum, and the lower lips of the coracoid groove (op. cit., Plate 41, fig. 1) are separated 

 by a primordial notch, whilst the earlier-formed inner lips are separated by a strong forthstanding, 

 flattened upper rostrum (see also Plate XVIII, fig. 2, r, of the present paper, to which my 

 references will now also be made). Behind the oblong, almost erect costal processes (c. p.), 

 there are three condyles for sternal ribs (s. r.) ; there are four in T. variegatus and brasiliensis. 

 Close behind the last condyle, the long outer xiphisternal bar (e. i. x.), which answers to the 

 forked bar of the Fowl, passes backwards, and is elegantly /-shaped. It is of extraordinary 

 length, and reaches, like the entosternum, to the same vertical line as the root of the tail. The 

 isthmus which connects the lateral parts to the ento-sternum is only half an inch in extent ; 

 thus the main part of the bone is divided into three very long narrow bands (see also op. cit., 

 Plate 41, fig. 1, e. s., hy. s.), the middle part being thrice the width of each of the delicate 

 sinuoso-arcuate bars. The keel (k.) is very deep, and does not retreat as in the Fowl, but stands 

 well forwards as in Hemipodiws (op. cit., Plate 35, fig. 5, e. s.), only a small space is left at its 

 anterior, somewhat acute angle, for the " pectoralis major" muscle ; nevertheless, as in the 

 " Raptores diurnae," these muscles swell far beyond the keel, and in actual mass are enormous. 

 Altogether, these muscles are, relatively, almost as large as in the Swift (Cypselus opus) ; but 

 their substance is pulpy, and their colour a faint greenish-white, quite Reptilian in character. 



Ordo" STRUTHIONINvE." 



Examples. Struthio camelus. Linn. ; Casuarius Bennettii, Gould ; Dromaus irroralus, Bartl. ; 

 Rhea Americana, Lath ; Apteryx Australis, Shaw. 



In the lowest types of Water-Birds (for example, the Penguin and the Cormorant), we 

 encountered nothing in the structure of the Shoulder-girdle that was not essentially typically 

 ornithic : here, however, in the true Ostriches, we have the simple characters of the Chelonian 

 Shoulder-bones back again. Now, it might be said that this was dependent upon the enfeebled 

 condition of the wings ; but this argument will not serve, for we have a similar Reptilian simplicity 

 in the Shoulder-plate of the Monotremes, and they have large fore-limbs. The earliest condition 

 that I have of these parts is in Struthio camelus (Struthio "A" of my paper on the Skull : see 

 'Phil. Trans.,' 1866); the embryo was the size of a Sparrow ; the figure (Plate XVII, fig. 5) is 

 magnified two diameters. The coraco-scapular cartilage answers very closely to that of an embryo 

 Tortoise, save that the scapula (sc.) is flattened; it is nearly as straight, has the same breadth, 

 and bifurcates in the same manner into a coracoid (cr.) behind, and a pra3-coracoid (p. cr.) in front. 

 The only trace of a meso-scapula is in the oval convexity which is seen mesiad of the glenoid 

 cup (gl.) ; but there is no other cleft than the one figured as almost dividing the two coracoid 

 bars ; this notch (cr. n.) enlarges above, but is a mere slit below. The pra?-coracoid is clubbed 

 below ; but the coracoid is pedate, the greatest enlargement being on the inner margin ; this 

 outspread front hook is large in the Monotremes, and has its own ectosteal bony patch the 

 epicoracoid : I have already described this inner hook in the Linnet. When the embryo half 



