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 BAL^NOIDEA, Whalebone, or True WJides. 1 



Family BAI^ENID^. 



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 vertebrae ; their capitular 

 processes, when present, not articulating directly with the bodies of 

 the vertebrae. 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 caecum. 



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. 2 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 



1 Icel. hvalr ; Dan. and Swed. hval ; Anglo-Saxon hwcel ; Germ, wal, 

 walfisch. The meaning apparently is "roller," the word being closely allied to 

 "wheel" (Skeat). 



2 These were discovered in the Greenland Whale by Geoffrey St. Hilaire, 

 whose observations were confirmed and extended to other genera by Eschricht. 

 They have been very fully described in Balcenoptera rostrata by Julin (Archivs 

 de Biologic, i. 1880). 



