402 THE ANATOMY OF VERTEBRATED ANIMALS. 



ribs blend together posteriorly. The symphysis of the 

 mandibles is extremely long and tlie jaws are narrow. Nu- 

 merous teeth with compressed fangs are f oiind in both jaws. 

 The eyes are small, and in Platanista they are rudimentary. 



In the DelphinidcB lastly (Dolphins, Porpoises, Gram- 

 puses), the teeth are usually ni;merous in both jaws, though 

 the Nai-whal is an exception to this rule, as has already 

 been mentioned. 



The anterior cervical vertebrse are generally ankylosed 

 together. The jDostei-ior ribs lose their capitula and become 

 articulated only with the transverse processes of the ver- 

 tebrse. The costal cartilages are well ossified. The sym- 

 physis of the mandible does not exceed one-third of the 

 rami in length, and the frontal and maxillary bones are 

 not especially produced upwards at their edges. 



As the common Porpoise {Phoccena communis), which 

 is a member of this grotip, is the Cetacean which is most 

 likely to come within reach of the student, it niay be useful 

 to speak at some length of its more interesting anatomical 

 peculiarities. 



The adult animal is usually about five feet long, and is 

 covered with a smooth integument upon which no hair 

 is to be discovered, though a few haii's are visible about 

 the mouth in the young animal. The contour of the 

 anterior part of the head is very convex, and presents, in 

 the middle line, the spiracle or blow-hole, which has the 

 form of a crescent with the points turned downwards and 

 foi-wards. The eyes are small and placed low down, close 

 to the posterior end of the gape of the mouth, which is 

 bounded by dense and rigid lips. The aperture of the ear 

 lies about an inch and three-quarters behind the eye, and 

 is so minute as to be discovered with difficulty. The 

 genital aperture is placed a long way in front of the anus 

 in the male ; while, in the female, the interval, in which the 

 fossae which lodge the teats are situated, is much less. 

 There is a conspicuous vertical dorsal fin in addition to the 

 flattened caudal fin. Immediately beneath the skin is a 

 thick layer of blubber, as in other Cetacea. 



