STRENTA 213 
or are only found in a most rudimentary condition, attached to the 
edge of the frontals, far away from the middle line; but in some at 
least of the extinct species these bones, though small in size, are 
normal in situation and relations. In very few other respects does the 
skull present any resemblance to that of the Cetacea. In the spinal 
column of existing forms none of the vertebrae are united together 
to form a sacrum, and the flat ends of the bodies do not ossify 
separately, so as to form disc-like epiphyses in the young state, as 
in nearly all other mammals; traces of epiphyses have, however, 
been recently detected in Afanatus, and they were fully developed in 
Halitherium and other fossil forms. The anterior caudal vertebre 
have well-developed chevron bones. In one genus (J/anatus) there 
are only six cervical vertebree. There are noclavicles. The humerus 
has a small but distinct trochlear articulation at the elbow-joint. 
The two bones of the forearm are about equally developed, and 
generally ankylosed together at both extremities. The carpus is 
short and broad, and the digits five in number, with moderately 
elongated and flattened phalanges, which are never increased in 
number beyond the limit usual in the Mammalia. The pelvis is 
extremely rudimentary, consisting of a pair of bones suspended at 
some distance from the vertebral column. In no existing species 
is there any trace of a hind limb, but in the extinct Halitherium 
an acetabular depression and rudimentary femur have been dis- 
covered. 
Two kinds of teeth, incisors and molars, separated by a wide 
interval, are generally present. The former may be developed into 
tusks in the upper jaw, or may be quite rudimentary. The molars 
vary much in character. In one genus (Lhytina) no teeth of any 
kind are present, at least in the adult. Some fossil forms show a 
more decidedly heterodont dentition, while Halitherium has milk- 
teeth, of which no traces have been observed in the recent genera. 
In all recent types the anterior part of the palate, and a corre- 
sponding surface on the prolonged symphysis of the lower jaw, are 
covered with rough horny plates of peculiar structure, which doubt- 
less assist in mastication. The tongue is small and fixed in position, 
with a surface resembling that of the plates just spoken of. The 
salivary glands are largely developed. The stomach is compound, 
being divided by a valvular constriction into two principal cavities, 
the first of which is provided with a singular glandular pouch near 
the cardiac end, and the second usually with a pair of elongated, 
conical, cecal sacs or diverticula. The intestinal canal is long, and 
has very muscular walls. There is a cecum, either simple, conical, 
and with extremely thick walls, as in Hualicore, or bifid, as in Aanatus. 
The heart is broad and flat, with its apex deeply cleft between the 
ventricles. The principal arteries form very extensive and complex 
retia mirabilia. The lungs are remarkably long and narrow, as, 
