390 



THE ANATOMY OF VEETEBEATED ANIMALS. 



male lias two tusk-like incisors whicli project from their 

 sockets in the premaxillse ; while, in the female, the tusks 

 remain concealed in their alveoli. 



In the festal state, both Halicore and Manatus have in- 

 cisors in the mandible as well as in the premaxillse. 



The stomach is divided into two portions by a median 

 constriction, and its cardiac end is provided with a peculiar 

 gland. Its pyloric end, in some species, gives off two cceca. 



There is a ccecum at the junction of the large and small 



intestine. Salivary glands are well developed. The apical 



portion of the septum, ventriculorum is deeply cleft, so that 



the ventricles are separated from one another through 



about half their extent. 



Fig. 10.3. 



Fig. 103.— Dorsal view of the heart of a Dugong (Halicore), its cavities 

 being laid open. JJ. i'., right ventricle ; /^. i., left ventricle. V.c.s.s, 

 left superior vena cava. F. c. s. d., right superior vena cava. V. c. i., 

 vena cava inferior. F. o. v., the inner end of a coecal diverticulum 

 of the right auricle, into which a style is introduced, and which 

 represents the foramen ovale. O., the auricular septum. 



There are two superior cavse and a Eustachian valve. 

 Extensive arterial and venous retia mirahilia are developed 

 in Manatus. In consequence of the great length of the 

 thoracic region and the brevity of the sternum, the dia- 

 phragm takes a very imusual course, extending veiy 

 obliquely from before backwards, and causing the upper 



