120 SHOULDER-GIRDLE AND BREAST-BONE. 



s upra- scapula ; they then suddenly widen behind, and narrow only a little downwards; they 

 are transversely cut and toothed to form a suture, where they meet at the mid-line. 



In the Chelonia (see Plate XII) the " inter-clavicle " is subject to the development of the 

 large bony plates that surround it ; it is therefore relatively rather small, for the bones in the bodies 

 of animals are like trees in a plantation ; their development depends upon the room they have for 

 expansion, and also in some degree upon the start the older trees get upon the newer. There is 

 something of this overshadowing in the inter-clavicle of the Chelonian ; but in the Lizard the 

 single bone has only two competitors ; and, posteriorly, it is free of all the ground. Now, this is 

 especially exemplified in Stellio, where the inter-clavicle is equal to one of the lateral bones in 

 the Chelonian, and is precisely such a radiating plate. Fig. 2 shows that the anterior knob is 

 trifid, and that the transverse bars are forked, the hinder spurs being only half the size of those 

 in front ; they both curve backwards, but the smaller forks to the greatest degree ; these clamp 

 the anterior part of the lower coracoid lips of the Sternum (Fig. 2, st.) ; those are tied fast to the 

 hinder and inner edge of the clavicles below. The whole of the posterior bar of this eight-rayed 

 inter-clavicle is applied to the under-surface of the anterior third of the Sternum ; it is shaped 

 like the blade of a dagger. 



The Sternum of Stellio (Plate' XI, fig. 2) is a forecast of what is found in the Bird ; some 

 of its most remarkable peculiarities, also, are to be seen in certain Mammals. The main part is 

 pentagonal, the antero- and postero- lateral margins being nearly equal, whilst the posterior trans- 

 verse margin is two thirds the extent of the "others ; the whole plate answers to the prse- and 

 meso-sternal regions of the Mammal. The posterior angles pass into the xiphisternajs (x. st.) by a 

 constricted isthmus. Most of the sternal regions of the Bird appear in this sternal plate, namely, 

 the coraco-, prae-, meso-, ento-, and xiphisternal regions. This is the first appearance of a mesial 

 part (e. st.), as separated from the lateral or costal regions ; and the extent to which this further 

 subdivision is carried in the Bird shows the great importance of the study of fenestra in 

 morphology, revealing the fact that they are not in the least accidental, and are true clefts, 

 although arrested at both ends. The large, sinous, double-lipped " coraco-sternal " edges (fig. 2), 

 meet at rather more than a right angle ; the Sternum is notched at the angle, and the right 

 side projects further beyond the notch than the left. The costal margins receive three pairs of 

 ribs, which are "thoracic;" and therefore the " pra3-sternum " reaches if compared with 

 the like part in the Human Sternum to the second rib ; and thus the meso-sternum has only 

 two ribs. The prse-sternal rib belongs to the ninth vertebra ; in front of it there are two equal 

 in size to its vertebral part, but they have no sternal piece ; in front of these we find the broad 

 cervical ribs of the sixth and fifth, the latter half the size of the former ; the first four vertebra 

 have no ribs. The " costal process " of the Bird's Sternum is not developed here; and the " ento- 

 sternum " (e. st.) is not produced either fore or aft, as in the Bird, where we have usually a large 

 " rostro- sternum " in front, and an immense development of the ento-sternum behind. This 

 first appearance of that most important element the " ento-sternum " is as a narrow flat band 

 (Plate XI, fig. 2, e. st.), small in size, undifferentiated at both ends, having neither rostral 

 process in front nor meso-xiphoid plate behind ; and without a trace of the " keel," so con- 

 spicuous in the Bird. It is cut off from the lateral parts of the Sternum by a long oval 

 fenestra on each side (st. f.) ; these fenestrse are nearly half as long as the Sternum ; their 

 first appearance here is as instructive as their last, where they spring up again in the Cheiroptera, 

 for instance, Plecotus auritus and Vespertilio murinus. The lateral " endosteal " plates have 



