PRIMARY GROUPS OF MAMMALS. 531 
form of the body being fish-like, aerate with a horizontal tail, and 
specialized for progression in the water. Periotic and tympanic bones 
anchylosed together, but not with sie squamosal. 
VII. ORDER SIRENIA. 
Brain narrow. Skull with the foramen magnum bream pmnp 
what downwards: supra-occipital nearly vertical and not extending 
T T the parietals meeting and interposed between it nae é fron- 
iotic with a posterior et rounded part; tympanic an- 
ie orm. Lower jaw with well-developed ascending rami and normal 
transverse condyles and coronoid processes. Lateral teeth. molar, and 
e m 
g 
aed 
» With the adjoining ones; and with normal digits. Mamme two, pectoral. 
Heart deeply fissured Neca the vent ri icles 
Contains four families one of which i$ datadi; and another probably, 
extinct. 
VIII. ORDER CETE. 
rain pae Skull with the foramen magnum entirely posterior, 
directed somewhat upwards BREE very large, sloping ee 
ae (attyp PONE sition ti torwa rds, over or between the fronta Peri- 
otic attenuated backwards; tympan e solia, entire. Lower ee with no 
ascending ramus, with its n UBTOW PERS s at the posterior extremities 
de u 
bones and phalanges often separated by cartilage; and with the sec- 
ond digit composed of more than three phalanges. Mamme two, in- 
guinal. 
Contains ten families, representing ret gr ZEUGLODONTIA 
with two families, both extinct; DENTICETĖ with six families, one of 
which is extinct; and MYSTICETE with es aii 
Super-Order Ineducabilia. 
Brain with a relatively small cerebrum, leaving behind much of the 
cerebellum exposed, and in front much of the olfactory lobes: corpus 
the vertical of the hippocampal sulcus, with no well defined rostrum in 
front. - 
(Insectivorous Series.) 
Teeth encased in enamel: incisors (very variable as to number) without 
persistent pulps: canines present (but sometimes modified in form) : mo- 
lars attypically with pointed cusps. Lower jaw with condyles transverse, 
received into special condyloid sockets. Placenta discoidal deciduate. 
scenester emda VOL. Y. 34 
