234 CETACEA 
and that they are the descendants of the Mesozoic reptilian order 
Ichthyopterygia, from which their hyperphalangism is a direct 
inheritance. The Ichthyopterygia have been shown, on very strong 
evidence, to have been derived from land reptiles, and to have 
gradually acquired their hyperphalangism as an adaptive character 
suitable to their peculiar mode of life, and there can be but little 
doubt that a similar adaptation has taken place in the case of the 
Whales. 
Suborder MYSTACOCETI, 
the BALENOIDEA, Whalebone, or True IV hates. 
Family BALZENIDA. 
Teeth never functionally developed, but always disappearing 
before the close of intra-uterine life. Palate provided with plates 
of baleen or “whalebone.” Skull symmetrical. Nasal bones form- 
ing a roof to the anterior nasal passages, which are directed upwards 
and forwards. Maxilla produced in front of, but not over, the 
orbital process of the frontal. Lachrymal bones small and distinct 
from the jugal. Tympanic bone involuted (Fig. 76), and ankylosed 
with the periotic, which is attached to the base of the cranium by 
two strong diverging processes. Olfactory organ distinctly de- 
veloped. Rami of mandible arched outwards, their anterior ends 
meeting at an angle, and connected by fibrous tissue without any 
true symphysis. All the ribs at their upper extremities articulating 
only with the transverse processes of the vertebra; their capitular 
processes, when present, not articulating directly with the bodies of 
the vertebr. Sternum composed of a single piece, and articulating 
only with a single pair of ribs. No ossified sternal ribs. External 
openings of nostrils distinct from each other, longitudinal. A short 
conical cecum. 
These animals have, when in the foetal state, numerous minute 
calcified teeth lying in the dental groove of both upper and lower 
jaws. They are best developed about the middle of foetal life, after 
which period they are absorbed, and no trace of them remains at the 
time of birth.? The baleen or whalebone does not make its appear- 
ance until after birth. It consists of a series of flattened horny 
plates, between three and four hundred in number, on each side of 
1Tcel. Avalr; Dan. and Swed. heal; Anglo-Saxon hwel; Germ. wal, 
walfisch, The meaning apparently is ‘‘roller,” the word being closely allied to 
“wheel” (Skeat). 
° These were discovered in the Greenland Whale by Geoffroy St. Hilaire, 
whose observations were confirmed and extended to other genera by Eschricht. 
They have been very fully described in Budwnoptera rostrata by Julin (Arechivs 
de Biologic, i. 1880). 
