312 



BRANCH CHORDATA 



and caudal. The cervical or neck vertebrae are nearly always 

 seven (there are six in the manatee, and six, eight, or nine in 

 some of the sloths). So the length of the neck depends upon the 

 length, not the number, of the vertebrae. The dorsal vertebrae 

 carry ribs and vary in number (from nine in Hypero'ddon 1 to 



MT 27 Na ME 



id 



Fig. 254. Skull of a dog, side view, with the right half of the mandible 

 or lower jaw and hyoid arch, the lower jaw displaced downward to show 

 its whole form. (Reduced), an, Anterior narial aperture; M T, maxillo- 

 turbinal bone; ET, ethmoturbinal; Na, nasal; ME, ossified portion of the 

 mesethmoid; CE, cribriform plate of the ethmoturbinal; Fr, frontal; 

 Pa, parietal; IP, interparietal ; SO, supra-occipital; ExO, exoccipital; 

 BO, basi-occipital; Per, periotic; BS, basisphenoid ; Pt, pterygoid; AS, 

 alisphenoid; OS, orbit osphenoid; PS, presphenoid; PI, palatine; Vo, 

 vomer; MX, maxilla; PMx, premaxilla (sh, stylohyal; eh, epihyal; ch, cera- 

 tohyal; bh, basihyal; th, thyrohyal) equal the right half of the hyoidean 

 apparatus; s, symphysis of the mandible; cp, coronoid process; cd, condyle; 

 a, angle; id, inferior dental canal; *, the part of the cranium to which the 

 condyle is articulated. (After Tenney.) 



twenty-two in Hyrax). The lumbar vertebrae also vary in 

 number, usually inversely, as the dorsal, their sum being rather 

 constant. The sacral vertebrae are fused together. They are 

 absent in Ceta'cea and Sire'nia, where there are no functional 

 hind limbs. The caudal vertebrae vary from three to fifty. 

 1 Beddard's " Mammalia," p. 23. 



