nAPLODONTID^— THOUAX OF HAPLODON RUFUS. 



r)77 



There are thirteen pairs of ribs. Tlic first ten ribs articulate (loubly 

 with the spinal culumn 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 vertebrie. The first nine ribs articulate l)y domi-facets at the 

 ends of the centra of two contiguous vertebrre, the first dcnii-fucel being upon 

 the seventh cermcul; the last four ribs articulate by full facets upon tlje ante- 

 rior margin of the corresponding last four dorsals. Seven ribs join the 

 sternum by means of their respective costal cartilages ; the first articulating p,t 

 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 obruptly 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 ,st t<i 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 tuber- 

 cle 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 ariiculation of the respective cartilages. 



Scapular arch. — The clavicle, about 1.10 long, is perfect, with articula- 

 tion at each end ; it is somewhat /-shaped in one profile, considerably curved, 

 ns well as flattened, at the ocromial end, which terminates with oblique artic- 

 ular face— the flattened part a little convex on one side and flat on the other — 

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