ii.] THE SPINAL SKELETON. 7I 



he shares with some animals (e.g. Apes and Cetaceans), though 

 sometimes, as in the Ungulata, it (as well as the second rib) 

 is almost straight. 



Occasionally, as in the Guinea Pig, Rhinoceros, and others, 

 the first rib bears a little spinous tubercle for the attachment 

 of the scalenus muscle. 



The ribs may consist not only of two parts, as in man, but 

 may have a third part intercalated between each vertebral 

 rib and its sternal cartilage or rib, as in the Monotremes, 

 Crocodiles, and many Lizards. 



The vertebral rib may give off (Fig. 77, a) a post-axially 

 projecting process (called uncinate), which may ossify as a 

 distinct bone, as is the case in most Birds and in the Crocodile. 



The sternal ribs may be cartilaginous or they may be 

 completely osseous. The latter, e.g., is the case in Birds and 

 the Armadillos. 



In shape they may differ much from man's, expanding 

 greatly, as is the case in the Great Armadillo and the 

 Monotremes. Each sternal rib may be set at a very marked 

 angle with its vertebral rib, as in Birds, instead of more or 

 less continuing its curve, as in man. 



Some of the sternal ribs may pass into each other (on the 

 ventral aspect of the body) directly without the intervention 

 of a sternum, or run right into the substance of the sternum, 

 as is the case with the more post-axial ribs of Chameleons and 

 some other Lizards. 



The sternal ribs may even slightly bifurcate at their ends, 

 as in the Tamandua. 



Bony sternal ribs may have, at their dorsal ends, synovial 

 articulations with the vertebral ribs, and also synovial articu- 

 lations with the sternum at their ventral ends, as in Birds. 



I 



FIG. 80. LATERAL VIEW OF SIXTH VERTEBRA OF SALAMANDRA. 



/, tubercular process ; c, capitular process the two supporting a rib which 



bifurcates at its free, distal end. 



The ribs may consist of single bones only, without any 

 division into vertebral and sternal portions, as in Fishes and 

 Batrachians. Ribs may also bifurcate distally, as in some of 

 the two last-mentioned classes (e.g. Salamandrd) ; and lastly, 



