* 
HAPLODONTID#—THORAX OF HAPLODON RUFUS. 5TE 
There are thirteen pairs of ribs. The first ten ribs articulate doubly 
with the spimal column by both head and tubercle; the last three by the head 
alone, there being no processes for articulation with a tubercle on the last 
three dorsal vertebra. The first nine ribs articulate by demi-facets at the 
ends of the centra of two contiguous vertebra, the first demi-facet, being upon 
the seventh cervical ; the last four ribs articulate by full facets upon the ante- 
rior margin of the corresponding last four dorsals. Seven ribs join the 
sternum by means of their respective costal cartilages ; -the first articulating at 
the top of the manubrium with the apices of the lateral process, the second 
to sixth at the successive nodes between two sternebers, while the end of the 
seventh reaches the sternum at the same point as the sixth, perhaps without 
true articulation, and certainly having no separate place of jointure. The 
eighth falls but little short of the sternum; the rest rapidly shorten. All 
the ribs bear costal cartilages, excepting, possibly, the thirteenth (last) one, 
which appears destitute of one. Taken either with or without their respect- 
ive cartilages, the ribs. rapidly increase in length from the first to the seventh 
or eighth, and then less rapidly decrease again, though the last, apparently a 
mere spicule without a cartilage, is abruptly shorter than the twelfth. Their 
curvature decreases continuously from first to last, and, in the same ratio, dis- 
tinctness of parts, including obliquity of neck to main shaft, diminishes; their 
tenuity increases from first to last. The bony part of the first rib is only 
half an inch long; the cartilaginous part is half as much more; these together 
complete about a semicircle. The bony part of the eighth is over two inches 
long; its cartilage is about one and three-fourths inches. On the anterior ribs, 
the neck stands very obliquely away from the shaft, the capitulum and taber- 
ele being both well marked. On the succeeding ribs which join the sternum, 
the neck simply continues the general curve of the shaft, here very consider- 
able. On the floating ribs, the neck similarly continues straight from the 
shaft, but the curvature is very slight. The under surface of most of the 
ribs shows the groove for the vessels; the posterior border is sharp; the 
anterior rounded; the sternal extremity expands and flattens (especially on the 
more posterior ribs) for the articulation of the respective cartilages. 
Scapular arch—The clavicle, about 1.10 long, is perfect, with articula- 
tion at each end ; it is somewhat f-shaped in one profile, considerably curved, 
as well as flattened, at the acromial end, which terminates with oblique artic- 
ular face—the flattened part a little convex on one side and flat on the other— 
7M 
