AQUATIC MAMMALS 



no clavicles, and all articulations of the forelimb except that of the 

 shoulder are fibrous and virtually immovable. The radius, ulna and 

 digital elements are greatly flattened, and the phalanges of the second 

 and third digit always exceed the normal number (hyperphalangism) . 

 The phalanges have epiphyses at both ends. The salivary glands are 

 rudimentary or absent. The diaphragm slopes greatly and extends far 

 backward. The vascular system is characterized by extensive retia mira- 

 bilia. The testes are abdominal. The internal ears are highly special- 

 ized. 



Odontoceti — the modern toothed whales, including the cachalot or 

 sperm whale. The integument of the throat never has numerous 

 grooves. The nostrils unite to form a single external orifice, within which 

 are a number of diverticula. The epiglottis is elongated and tubular. 

 Teeth are present and there is no baleen. The olfactory apparatus is ab- 

 sent or extremely rudimentary. The skull is asymmetrical, the right 

 side being more developed than the left, the nasal bones are rudimentary 

 and the telescoping of the skull is mainly from before posteriorward. 

 Mediad of the angle of the mandible there opens a large space into 

 which fits a specialization consisting of fatty tissue and trabeculated air 

 passages opening from near the Eustachean tube (this may not be pres- 

 ent in some sorts) . More than one pair of ribs articulate with the ster- 

 num, which is composed of more than a single bony element (although 

 these may fuse in adults) . The muscles of the lower arm are very ru- 

 dimentary and the digits always number five. There is no vestige of 

 the femur present except in the sperm whale. There is no caecum ex- 

 cept in the Platanistidae. 



Mysticeti — the whalebone or baleen whales. The integument of the 

 throat has deep longitudinal grooves in some genera, but not in others. 

 The nostrils have two distinct openings. The epiglottis is not espe- 

 cially elongated. Teeth are present only in the fetal state, adults hav- 

 ing the roof of the mouth furnished with plates of baleen or "whale- 

 bone." The olfactory organ is much reduced but is present. The skull 

 is symmetrical, its chief peculiarities for the present purpose being the 

 development of the rostrum for the accommodation of the baleen, the 

 elevated position of the nares, and the marked anterior inclination of 

 the occipital shield, the telescoping being mainly from behind anterior- 

 ward. The nasals are much reduced but are not strictly rudimentary. 

 But one pair of ribs articulates with the sternum, which is composed of 

 only the manubrium. The muscles of the lower arm are not as much re- 

 duced as in the Odontoceti and the digits number either four or five. 



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