80 The Alligator and Its Allies 
mediate portion is present in all but the tenth rib, 
and wherever present, except in the ninth rib, 
it articulates distally with the sternal portion. 
The sternal portions extend medio-cephalad in a 
direction atright angles to the intermediate portion ; 
the first two articulate with the sternum, the next 
six with the xiphisternal horns, and the ninth and 
tenth are missing. 
The Abdominal Ribs (Fig. 26, 4). While these ribs 
are membrane bones and are not homologous with 
the other ribs, they may as well be mentioned at 
this time. They consist of about seven V-shaped 
sets of slender bones, the point of each V being 
directed cephalad. Each V is made up of from 
two or five slender bones, the number and arrange- 
ment being subject to considerable variation. 
The last V of the series (not well shown in the 
figure) is considerably larger than the rest and is 
made up of four curved bones that extend around 
the anterior ends of the pubic bones and are united 
to them by a broad tough membrane. The first or 
most anterior V is united by a narrow membrane 
(not shown in the figure) with the membrane that 
extends between the xiphisternal horns. All of 
the V’s are more or less connected with each other 
by fibrous membranes. Since these ribs lie super- 
ficial to the recti muscles of the ventral body wall 
they are sometimes missing in carelessly prepared 
skeletons. 
The Sternum (Fig. 26). The sternum consists of 
