THE BRITISH MAMMALS : ORDERS, FAMILIES, ETC. 21 



first caudal being distinguishable by the chevron bone on its under 

 surface. There are no external ears ; the eye is small ; the nostrils 

 open out near the top of the head, either separately or by a single 

 orifice. The brain is fairly large, its case almost spherical. The 

 facial region of the skull is well developed ; the supra-occipitals rise 

 to meet the frontals by growing over or in between the parietals, 

 the frontals being expanded laterally to roof over the orbit. In 

 front of the narial aperture a beak, consisting of the maxillae, 

 premaxillae, vomer, and mesethmoid cartilage, extends forward to 

 form the roof of the mouth. The teeth range from none to many in 

 the adult, but before birth exist in all species. The skin is almost 

 hairless, hairs in the adult appearing only near the mouth. The 

 mammae are two in number, and situated in depressions on each side 

 of the genital aperture ; from them the milk is injected into the 

 mouth of the young so as to lessen the difficulty of sucking under 

 water. There are three sub-orders the Mystacoceti, or whalebone 

 whales; the Odontoceti, or toothed whales; and the Archaeoceti, 

 containing only an extinct genus in which the te-eth, unlike those of 

 the Odontoceti, are divisible into incisors, canines and molars. Of 

 the first we have the one family Balsenidas to deal with ; of the 

 second we have the Physeteridaa and the Delphinidse. 



In the Balaenidas, the whalebone takes the place of teeth, these 

 being absorbed before birth. The skull is symmetrical and more or 

 less arched ; the maxillae does not overlap the orbital process of the 

 frontal ; the branches of the lower jaw arch outwards, and are 

 generally united only by a ligament. The sternum is in one piece, 

 and articulates with one pair of ribs ; the ribs articulate only with 

 the transverse processes of the vertebras. There are two blowholes. 

 This family is represented in the British list by three genera, 

 Balczna, Balcsnoptera, and Mcgaptera (Plates xix., xx., and xxi., 53 

 to 58). 



In the Physeteridae there is no whalebone. The teeth in the 

 upper jaw are generally absent or rudimentary, those in the lower 

 jaw are fully developed. The skull is not symmetrical, the maxillae 

 overlap the orbital process of the frontal ; the branches of the lowei 

 jaw are nearly straight, and form a true symphysis. The sternum 

 is in several pieces, and articulates with several pairs of ribs ; the 

 ribs in its vicinity articulate with the bodies of the vertebrae. There 

 is only one blowhole. Of this family there are four genera on our 

 list Hyperoodon, Mesoplodon, Physeter, and Ziphius (Plates xxii. 

 and xxiii., 59 to 62). 



The Delphinidse differ mainly from the Physeteridae in having 

 teeth in both jaws, the teeth as a rule being numerous, and in 

 having the anterior ribs attached to the bodies of the vertebrae by 

 their heads, and to the processes of the vertebrae by a tubercle, 

 while the hinder ribs are attached by the tubercle only. There 

 are nine British genera Delphinapttrus, Delphinus, Globicephalus, 

 Grampus, Lagenorhynchus, Monodon, Orca, Phoccena, and Tursiops 

 (Plates xxiv., xxv., xxvi., 63 to 72). 



There are thus only eighteen families represented among the 

 Pritish mammals, a number so small that, instead of devoting a 



