CHAP, xiii.] THE CAT'S PLACE IN NATURE. 463 



especially to the distal segment of the arm, which corresponds to 

 the fore-paw of the cat. The lower parts of the legs are clothed 

 with horny scales. 



In internal structure, the main characters agree with those of the 

 cat, but there are a multitude of differences. The more significant 

 of these are as follows : The thoracic and abdominal cavities are 

 not quite separate, the diaphragm forming only an incomplete 

 partition. 



The cervical vertebrae are thirteen and the dorsal eight, and 

 behind these no less than ten, at the least, are fused with the pelvis 

 into a great solid sacral mass which includes even the last two 

 dorsals. The caudal vertebrce are few and end in a bone, shaped 

 somewhat like a ploughshare, called the zygostyle. 



The ribs which are connected with the sternum are connected 

 with it, not by the intervention of costal cartilages, but by long 

 narrow bones (sternal ribs) instead. 



The sternum consists mainly of a great flattened quadrangular 

 sheet of bone, from the middle of the ventral surface of which a 

 long and strong keel projects, supporting a mass of flesh which lies 

 on each side of it, and which is related to the power of flight. 



The skull has but one occipital condyle, and the front apertures 

 of the nares are placed some distance back from the front end of the 

 skull one on each side of the bony beak. No zygoma passes back 

 from the hinder margin of the orbit, but a needle-like bone bounds 

 the orbit externally below, passing backwards from the beak to 

 abut against a movable complexly shaped bone the os quadmtum. 

 Inside the skull there is no cribriform plate, but only a foramen for 

 the nerves of smell, while the bony palate shows some large open- 

 ings, two of these being the posterior nares. The periotic bones 

 unite with other cranial elements before uniting together. 



The lower jaw, toothless like the upper, is made up of several 

 bones on each side. It does not join the squamosal, but fits, by an 

 irregularly shaped hollow cup, to the lower part of the os qua- 

 dratum. 



The shoulder-girdle is complete. Instead of each blade-bone 

 having only a small coracoid process, there is, as in the lizard, a 

 large and distinct coracoid-bone, which passes down from the slender 

 blade-bone to abut against the breast- bone, and the arch is further 

 complete by the clavicles which, instead of being two separate 

 slender little bones embedded in the flesh alone, here form the 

 merrythought QI furculum, which above abuts against the coracoids 

 and scapula, and below is firmly fixed to the sternum. 



The anterior extremity of the pectoral limb is greatly reduced, 

 exhibiting only rudiments * of the parts we saw in the cat's fore- 

 paw. 



The pelvic girdle is at once more complex and less complete than 



* There are two carpal bones ; three i two are separate save at their ends), and 

 metacarpals united in one mass (though I three digits with one or two phalanges. 



