1I SKULL OF MAMMALS AND REPTILES 25 
particularly conspicuous in the Whales and in the Edentates. In 
the former group the occurrence of the first intercentrum serves 
to mark the separation of the caudal from the lumbar series. 
The number of caudals varies from three in Man—and those 
quite rudimentary—to nearly fifty in Manis macrura and Micro- 
gale longicaudata., 
The Skull. —The skull in the Mammalia differs from that 
of the lower Vertebrata in a number of important features, which 
will be enumerated in the following brief sketch of its structure. 
Fic. 14.—Lateral view of skull of a Dog. C-occ, Occipital condyle; F, frontal ; 
F.inf, infra-orbital foramen; Jg, jugal; Jm, premaxilla; JZ, lachrymal; J, 
maxilla; Mazd, external auditory meatus; Md, mandible; N, nasal; P, 
parietal; Pal, palatine; Pjt, process of squamosal; P#, pterygoid; ph, ali- 
sphenoid ; Sg, squamosal; Sq.cce, supraoccipital; 7, tympanic. (From Wieder- 
sheim’s Comparative Anatomy.) 
‘In the first place, the skull is a more consolidated whole than in 
reptiles; the number of elements entering into its formation is 
less, and they are on the whole more firmly welded together 
than in Vertebrates standing below the Mammalia in the series. 
Thus in the cranial region the post- and pre-frontals, the post- 
orbitals and the supra-orbitals have disappeared, though now and 
again we are reminded of their occurrence in the ancestors of 
the Mammalia by a separate ossification corresponding to some 
of. the bones. Nowhere is this consolidation seen with greater 
clearness than in the lower jaw. That bone, or rather each 
half of it, is in mammals formed of one bone, the dentary (to 
which occasionally, as it appears, a separate mento-Meckelian 
