REPTILES. Ill 



thickens from below upwards to stop this gap in the Sternum. The four anterior cervical 

 vertebrae of Leemanctus have no free ribs ; the next two have each a pair of floating ribs, tipped 

 with cartilage, and three or four lines in length. The seventh and eighth have ribs equal to those 

 of the dorsal region, namely, seven lines long, and well ossified, with a small triangular epiphysis 

 at the end; and these turn towards each other, below (fig. 7, c. 7, c. 8): the ninth vertebra is the 

 first dorsal. Four pairs of dorsal ribs have semi-osyous sternal portions which articulate by 

 perfect (synovial) joints with the long sides of the Sternum. 1 The narrow posterior end of the 

 Sternum is entirely occupied with the large xiphisternal horns (x. st.), the broad single portion 

 of which is three lines in extent ; the forks into which these break are the fifth and sixth 

 sternal ribs (fig. 7) : these have no "costa intermedia" constricted from them, nor have the 

 preceding four. The sternal horns are continuous with the meso-sternum, but there has been an 

 attempt at segmentation in the form of a lateral vertical groove (fig. 7, st. x. st.), and there is a 

 clear space of unossified cartilage between the endosteal deposits. In the prae-meso-sternum 

 clear cartilage is seen marginally, round the fontanelle above, and also near the "horns" 

 (fig. 9) below ; the lower internal bony plate is quite divided into two equal halves (fig. 8). 

 The sternal ribs, like the xiphisternal horns, are composed of a tube of soft cartilage, having in it 

 a tube of bone ; and lastly, an axial pith of soft cartilage ; this, however, is common to the 

 Lacertilia. The clavicles (cl.) of Ltemanctus are elegant/-shaped bars, narrow and pointed where 

 they join the base of the supra-scapula, and expanded below : in the expanded part there is an 

 open membranous space (figs. 7 and 8). The "inter-clavicle" (i. cl.) is a long, very elegant, 

 cross-shaped bone, the transverse bars of which are three lines in extent, and the longitudinal 

 part nine lines long. The lower surface of the bone projects, anteriorly, as a crescentic ridge bound- 

 ing the groove in which the clavicles lie, but do not quite meet (fig. 8) ; above (fig. 9), there is a 

 rounded ridge, with a blunt end : the transverse bars are also knobbed at their ends, and they turn 

 a little backwards. Behind these bars the main part is constricted; it then widens gradually to 

 the middle, and as gradually becomes attenuated to a blunt point (fig. 8). It is flat above (fig. 9), 

 convex below (fig. 8), and becomes thickened, vertically, where it shuts up the sternal fontanelle (fig. 9, 

 i. cl.). This is the longest "inter-clavicle" I have to describe, for it reaches to between the 

 second pair of ribs : in Monitor draccena it is very long, but only reaches to between the first pair. 

 We shall see the inter-clavicle wedging itself between the sternal moieties again in the Grallse 

 amongst the Birds (e.g. Grus montignesia, Plate XIV., figs. 6 and 7). In ascending from Class 

 to Class we are never safe from the repetition of some morphological habit, which, being the rule 

 in the lower types, characterises them, but recurs exceptionally higher up. This affinity of the pos- 

 terior part of the inter-clavicle for the divisional line of the Sternum may be said to be a Reptilian 

 character ; but whenever this part is sufficiently developed in Birds we then find that it recurs. 



Example 3. Cyclodus nigroluieus, Quoy and Gaimard. 



The mailed Cyclodonts yield examples of Shoulder-girdle and Sternum no less instructive 

 than those of the Iguanians ; and they especially serve to show what becomes of the pair of forked 

 xiphisternals in the next metamorphic stage to that last described. Plate X, figs. 1 and 2, show 



1 Fig. 8 does not show the left side of the Sternum so short as it ought to have done ; Fig. 9 

 shows it better. 



