skp:leton of aetiodactyla. 



465 



formula is: — 7 cervical, 14 dorsal, 5 lumbar, 4 sacral, and 11 

 caudal. The pleurapopliyses of the third, fourth, and fifth 

 cervicals are developed forward as well as backward ; those of the 

 sixth are also of great breadth, and are more joroduced downward. 

 The metapophysis is distinctly developed upon the second and 

 succeeding dorsal vertebrae, and attains the outside of the zyga- 

 pophysis in the eleventh. All the dorsal ribs are biarticulate, re- 

 taining both head and tubercle. Eight pairs of ribs directly join 

 the sternum, which consists of seven bones. In the Megaceros, 

 fig. 166, as in the Fallow and most other Deer, there are thirteen 

 dorsal and six lumbar vertebras. 



The opisthoca3lian ball-and-socket joints of the cervical ver- 

 tebrae facilitate the habitual inflections of the neck in the grazing 

 and browzing actions in all Kuminants, while the long spines of 

 the anterior dorsals afford adequate surface of attachment to the 

 elastic and muscular structures sustaining the head — heavy in 

 most of them with horns or antlers. 



B. Skull. — This presents great diversity of shape in the Artio- 

 dachda, ^\\i\\ some common 



312 



characters, already noted, 

 which distinguish it from 

 that of Perissodactyla. 



In the Hippopotamus, 

 fig. 312, the occiput is sub- 

 vertical : from the upper 

 part of its crest the con- 

 tour of the skull runs 

 nearly straight to the fore 

 ends of the nasals, 1 5. The 

 orbits, small and with an 

 entire, or almost entire, rim 

 of bone, singularly project both upAvard and outward, the frontals, 

 11, rising toward them, and arching lengtliwise across their upper 

 half. The upper jaw, c, which is almost cylindrical in advance of 

 the molar series, suddenh^ expands to form the alveoli of the upper 

 tusks, the mandible similarly expanding for those of the lower 

 tusks, c ; in the upper jaw a second terminal expansion, divided by 

 a deep groove from the first, increases the space for the large tusk- 

 shaped incisors. The depth of the temporal fossai renders that part 

 of the cranium, 7, narroAver across than any part of the face : the 

 fossae meet above to form a parietal crest in old males. The facial 

 part of the lacrymal is extensive, but the small deep-seated orbital 

 part is perforated by the lacrymal foramen. The malar, 26, sends 



VOL. IT. H H 



Hippopotamus amphibius. 



