BIRDS. 179 



ectosteal layer forms a jagged ring round the neck of the scapula, and a larger ensheathing 

 bony layer has appeared round the body of the coracoid (cr.). This latter part is moderately 

 broad, and has its head down-turned in front, and its epicoracoid base (e. cr.) greatly expanded. 

 From the meso-scapular projection (m. sc.) there has been segmented a tear-shaped mass of soft, 

 clear cartilage, the " meso-scapular segment" (m. sc. s.), and from the down-turned head of the 

 coracoid a heart-shaped segment of somewhat denser hyaline cartilage has been freed : this is the 

 prse-coracoid segment (p. cr. s.). In the perichondrial stroma (p. r.) which passes as a band 

 downwards towards the mid-line of the body, there has been a styliform mass of bony matter 

 deposited : this is the first appearance of the clavicle (cl.) ; it is altogether distinct in substance 

 and in essence from the two cartilaginous segments. At this time the two halves of the Sternum 

 have begun to coalesce, their outer margins having already been cleft from the sternal ribs. In a 

 few more days, two or three before hatching, the embryo has undergone great changes ; these are 

 figured in Plate XV, figs. 13 15 (fig. 13 is magnified eight diameters, and figs. 14 and 15 

 twenty-four diameters). The scapula (sc.) has acquired a more perfect shaft, and is more that 

 of the adult, so also is the coracoid (cr.) : both these parts are much more slender, and like 

 the finished bone of the adult. The clavicle (cl.) has reached its fellow below, and at this 

 junction an inter-clavicle (i. cl.) has been formed ; above, the clavicle has entered the meso- 

 scapular segment (m. sc. s.), ossifying it, and being at present surrounded by it upon the upper 

 third, the hyaline cartilage forming an embracing loop, which will soon be converted into the 

 upper part of the furcular ramus. The prse-coracoid segment (p. cr. s.) is co-extensive, vertically, 

 with the meso-scapular ; but it juts out transversely into a large rounded lobe of flat, consistent, 

 hyaline cartilage, like the blade of a hatchet, with the edge, however, lying against the haft (figs. 14, 

 1 5) ; for since the last stage this piece has grown forward so as to lie in front of the clavicle, to 

 the antero-external edge of which it is attached by connective tissue. This autogenous prse- 

 coracoid continues soft until the young Bird is wellnigh fledged ; the mode of its ossification is 

 endosteal, as is shown in the furcula of Corvus monedula (fig. 19, p. cr. s., cl.) : in a few weeks, 

 after becoming quite ossified, it coalesces with the clavicle, to form the anterior lobe of the two- 

 eared furcular ramus. 1 The tissue round the inter-clavicle is not sufficiently developed in the 

 Passeringe to show a distal prae-coracoid, although this is the part where it should appear, and 

 where it can be demonstrated in the Gallinsc. The Sternum of the Linnet at this stage is very 

 similar to that of the adult ; the rostrum (r.) is long and well forked ; the costal processes (c. p.) 

 are broad and oblique ; the keel (k.) is at present low ; the narrow external xiphoids (e. x.) are very 

 divergent ; the middle xiphoid (m. x.) has a large primordial notch, and the coracoid grooves 

 (cr. g.) are well-grown and distinct from each other, a notable raphe being visible between them 

 at the mid-line. In the adult all the parts have become intensely ossified in condition, and 

 extremely elegant and slender in form ; the scapula has become a very narrow, curved, pointed 



1 The compound nature of the Passerine furcula was long since known to Nitzsch. (See his 

 article " Passer ince," Ersch und Griiber, ' Encyclopadie/ Section iii, Theil 13, 1840.) He says, 

 " In all Passerinse the furcula is very remarkable for a lamellar handle (Griff), directed backwards, and 

 for expanded hammer-shaped upper ends. This expansion of the upper ends arises from the addition 

 of a special bone, which eventually coalesces with the furcula, which I have called epicladium, and 

 with which Geyffroy St. Hilaire was already acquainted. It is found elsewhere only in the Wood- 

 peckers and the King-fishers." This restriction of the development of the " epicladium" (proximal 

 pr EC- coracoid) is a mistake; it is generally present in the Carinatse. 



