CETACEA 



the ribs with hut a single head. Sternum is short, broad, and consisting of one piece 

 and joined only to the foremost ribs. 



The baleen whales are the most remarkable and highly specialised group 

 of Cetacea on account of the degeneration of the 

 jaws and the development of baleen in place of teeth. 

 The only indication that this form is derived from 

 toothed ancestors is the occurrence of small, weak 

 teeth hidden in the gums of the embryo. In skull 

 formation, especially in the development of nasals, 

 frontals and parietals, the Mystacocetes are more 

 primitive than the Odontocetes. 



Family 1. Balaenopteridae. Fin Whales. ^ 



Head less than one-fourth of the total length of the 

 whole body. On the lower side of the body there are many 

 furrows. Dorsal fin present. Manus with four digits, 

 narrow and rather long. Baleen short and broad. 

 Cervical vertebrae articulating, not fused, their centra 

 rather long. Tympanic long and much inflated and 

 rounded on all sides. Recent and fossil in the 

 Miocene and Pliocene. 



Plesiocetus v. Bened. (Fig. 113). In the Miocene 

 of France and southern Germany. Complete 

 skeletons 6 m. in length have been found in the 

 Pliocene of northern Italy. 



C'etotherium Brandt (Aulocetus v. Bened.). Miocene. 

 Heterocetus, Herpetocetus, Mesocetus van Bened. 

 Balaenoptera Lacep. Mcgaptera Gray, in the Plio- 

 cene of Belgium and England. A complete 

 skeleton of Mesocetus has been found in Hungary, 

 Sopron County. 



From the Miocene of North America Siphono- 

 cetus, Cetotherium and Mesoteras Cope are known. 



Familj' 2. Balaenidae. Right Wliales. 



Skull very large, comprising, at least, onefourth of 

 the entire length of the body. Skin on the ventral surface 

 smooth. No dorsal fin. Manus with five digits, broad 

 and foreshortened. Baleen very long and narrow. Lower 

 jaw narrow, very convex, jlattened on the inner side and 

 having spherical condyles. All, or almost all, of the 

 cervical vertebrae are fused. Lumbar and caudal vertebrae 

 short. Tympanic almost square and angular and but 

 slightly inflated. 



Fio. 113. 



Plesiocetus cuvieri Desm. Plio- 

 cene of Monte Puguasco near 

 Piacenza. 1/^. (After Cnvier.) 



The Eight Whales are restricted at the present 

 day to the Polar regions of both hemispheres. Fossil forms of the genus 



