228 Zoological Society. 



carotid and left subclavian have more obviously separate origins'. The 

 aorta suddenly diminishes beyond those primary branches, where it 

 is connected with the consolidated and contracted ' ductus arteriosus.' 

 There is no arrangement, even in the very young Walrus here de- 

 scribed, for accommodating the animal to its aquatic habits, by any 

 direct intercommunication between the right and left sides of the 

 heart. The hepatic veins, in their dilatations, resemble those of the 

 ordinary Seals. 



The brain weighed 1 lb. 9 oz. avoir. ; its convolutions and struc- 

 ture were described. The hip-joint was found to be devoid of the 

 ligamentum teres. Drawings were exhibited of the viscera of the 

 thorax and abdomen, and the Memoir was terminated by a minute 

 account of the dentition, and a disquisition on the homologies of the 

 teeth of the Walrus, as elucidated by the state of the dentition in the 

 young animal dissected. 



Professor Owen detected the following minute teeth exposed or 

 buried in the gum, and adhering to the gum and periosteum of the 

 jaws : — two denticles in each premaxillary bone ; two denticles in 

 each maxillary bone ; together w ith a deciduous canine, and four den- 

 ticles in each ramus of the mandible. He gave the following as the 

 formula of the deciduous dentition of the Walrus : — 

 . 2—2 i~2}_ 



* ^Z^> ^ 0-0' 



Of the permanent series, the canine tusks had pushed through the 

 gum, and on laying open the substance of the jaws, the following 

 teeth were found in course of formation : — in the premaxillary, the 

 successor of the second minute incisor ; in the maxillary, the succes- 

 sors of the two deciduous molars, together with a third molar. In 

 the lower jaw the successor of the second deciduous incisor, the suc- 

 cessors of the two deciduous molars, and a third similar permanent 

 molar. The germ of the permanent tusk, confined to the upper 

 jaw, was 2 inches in length, and, like the germs of the smaller per- 

 manent teeth, its base was widely open, and contained a large forma- 

 tive pulp. 



In addition to the upper canine tusks, the normal number of per- 

 manent and functional teeth in the Walrus is four on each side of 

 both jaws ; these teeth are simple, short, thick and obtuse, having 

 the office of grinders. With respect to their nature and homologies, 

 Professor Owen argued that the first, from its position in the pre- 

 maxillary bone, was an 'incisor'; the two following teeth, by their 

 position in the maxillary bone, and their relation to the deciduous 

 denticles, were 'premolar' teeth; and he also regarded the last of 

 the series of four, from its minor degree of development, as belong- 

 ing rather to the same (premolar) series, than as being the first of 

 the true molars. As the first of the molariform permanent teeth in 

 the lower jaw passes in front of the permanent incisor above, when 

 the mouth is closed, it must be regarded as an ' incisor ' ; the other 

 three grinders as being ' premolars,' two being proved to be such by 

 displacing vertically their predecessors, and the third also appearing 

 to be of the same series by its state of development. The Professor 



