112 ELEMENTS OF MAMMALIAN ANATOMY. 
number of teeth in the different genera varies considerably, 
as seen by the following formula: 
PIG, & Been eee aeawialei a chevh dace oaenecereins i#,ct,p4,m $= 44 
DO atte aioe la An stieay inate ens coaiiaa sel te i8,ci,p 4 m2= 42 
Cate roman he au saints aes meee en i3,ci,p 4, mi = 30 
Porcupine s.:.:¢senes, aenvennwneses it,c,p4, m #=20 
HEED. opcode ys cy slat stares one ave ue mannass i%,c%p % m 3 = 32 
Ores circu a ead a Aaawetaaeeran ae: i3g,cijp4m3=44 
Opossumy ne ncc ev bce ane Weeee went oe i4,ci,p#,m4=50 
Miah, ig. ase hee Sarat su slawnsies inca i3,c4,p 3, m $= 32 
The elephant presents a very specialized dentition. It 
has no canines nor any lower incisors. The single pair of 
upper incisors is developed into long tusks, much prized for 
ivory. They continue to grow throughout the entire life 
of the animal. Six molars are present on each side, only 
one or two of which are functional at once. The posterior 
ones move forward to take the place of the anterior as these 
become worn out. The tusks of the walrus are its canines 
greatly developed. None of the typical modern Ruminants 
have upper incisors in the adult state, though they are 
present in the embryo. Palzontology has demonstrated 
that the ancestors of the Ruminants had well-developed 
upper incisors in the later Eocene times. The occurrence 
of the rudimentary upper incisors in the embryo furnishes 
evidence of a full dentition in the ancestors of the rumi- 
nants, since the individual embryological history is some- 
what of a recapitulation of the ancestral history of the race. 
THE PHARYNKX. 
The pharynx is that portion of the alimentary canal be- 
tween the mouth and the esophagus. The structure is well 
shown by making a sagittal section through the head and 
neck. This is best done with a saw, after the specimen is 
frozen by placing it out-of-doors during one or two days 
of cold winter weather. 
