TEETH. 



915 



"sectorial" or " carnassial ; " but we may 

 point with certainty to the third molar above 

 and the fourth below as answering to those 

 teeth which manifest the sectorial character 

 in the terrestrial Carnivora. 



The coadaptation of the crowns of the 

 upper and lower teeth is more completely 

 alternate than in any of the terrestrial Car- 

 nivora, the lower tooth always passing into 

 the interspace anterior to its fellow in the 

 upper jaw. In the genus Phoca proper (Ca- 

 locephalus, Cuv.) typified by the common seal 



(1'h. vitiilina), the dental formula is, i. Q , 



11 33 22 _ 



and proportions of these teeth are shown 

 in PI. 132, fig. !., of my "Odontography." 

 The first tooth above and below presents a 

 complete confluence of the fangs ; they are 

 separated from the second above ; but be- 

 low they sometimes do not become free 

 before the fourth, and sometimes the two 

 roots are distinct in the third and second 

 molars. In the Phoca ancllata Nills., the 

 principal cusp of the molar teeth is com- 

 plicated with anterior and posterior smaller 

 cusps, sometimes one in number in the upper 

 molars ; the anterior accessory cusp is some- 

 times wanting in the first, and is rudimentary 

 in the rest ; but usually there are two small 

 cusps behind the principal one, and in the 

 three or four posterior molars in the lower 

 jaw there are sometimes two small cusps be- 

 fore and two behind the principal one.* 



In the Phoca caspica the upper molars have 

 commonly one accessory cusp before and one 

 behind the principal lobe ; the lower molars 

 have one accessory cusp before and two be- 

 hind. 



In the Phoca gr&nlandica, the upper molars 

 have no anterior basal cusp and only one be- 

 hind ; the lower molars have two cusps behind 

 and one in front, except the first, which re- 

 sembles that above, and, like it, has connate 

 fangs. 



The condition of the molar teeth is nearly 

 the same in the Phoca barbata, but the crowns 

 are rather thicker and stronger, and the three 

 middle ones above have two posterior basal 

 cusps feebly indicated, the same being more 

 strongly marked in the four last "molars 

 below. 



The following genera of seals with double- 

 rooted molars (Pelagius and Stenorhynchus) 



have four incisors above as well as below, i. c. 



2 9 



a~ a- An upper view of the molar teeth in 



the Hooded Seal of the Mediterranean (Pcla- 

 gius monachits) is given in my Odontography, 

 PI. 132. fig. 3., as when they are worrT down 

 in an old specimen ; the crowns are thick, 

 obtuse, sub-compressed, with a well developed 



* Nillson, in Wiegmann's Archiv. 1841, 313. I 

 notice these varieties of the crown, in connection 

 with analogous ones in the fangs of the teeth of the 

 same species, to show the inadequacy of such cha- 

 racters as marks of subgeneric distinction. 



cingiilum, a principal lobe and an anterior and 

 posterior accessory basal lobule ; the fangs 

 are connate in the first tooth both above and 

 below. 



The allied sub-genus (Ommatophoca) of seals 

 of the southern hemisphere has six molar 

 teeth on each side of the upper, and five on 

 each side of the lower jaw, with the principal 

 lobe of the crown more incurved. The two 

 first molars above are closely approximated, 

 but this may prove to be a variety. 



In the Stenorhynchus the jaws are more 

 slender and produced, and the molar teeth are 

 remarkable for the long and slender shape of 

 the principal lobe, and of the accessory basal 

 cusps. The incisors have sharp conical re- 

 curved crowns, like the canines, and the ex- 

 ternal ones in the upper jaw are intermediate 

 in size between the canines and the middle in- 

 cisors. 



In the Stenorhynchus leptonyy each molar 

 tooth in both jaws is trilobed, the anterior 

 and posterior accessory curving towards the 

 principal one, which is bent slightly back- 

 wards ; all the divisions are sharp-pointed, 

 and the crown of each molar thus resembles 

 the trident or fishing-spear ; the two fangs of 

 the first molar in both jaws are connate. In 

 Stenorhynchus serridens the three anterior mo- 

 lars on each side of both jaws are four-lobed, 

 there being one anterior and two posterior 

 accessory lobes ; the remaining posterior 

 molars (true molars) are five-lobed, the prin- 

 cipal cusp having one small lobe in front, and 

 three developed from its posterior margin ; 

 the summits of the lobes are obtuse, and the 

 posterior ones are recurved like the prin- 

 cipal lobe. Sometimes the third molar be- 

 low has three instead of two posterior acces- 

 sory lobes. Occasionally, also, the second, as 

 well as the first molar above, has it fangs con- 

 nate ; but the essentially duplex nature of 

 the seemingly single fang, which is unfailingly 

 manifested within by the double pulp-cavity, 

 is always outwardly indicated by the median 

 longitudinal opposite indentations of the im- 

 planted base. These slight and unessential 

 varieties, presented by the specimens of the 

 Saw-toothed Sterrink (Stenorhynchus serridens) 

 brought home by the enterprising Naturalist 

 of Sir J. Ross's Antarctic expedition, accord 

 with the analogous varieties noticed by the 

 best observers of the seals of our neighbour- 

 ing seas, as, for example, Nillson. 



The Grey Seal (Haiichaerus gryphtis) of our 

 own seas begins, by the extension of the 

 connate condition of the two roots through a 

 greater proportion of the molar series^ to 

 manifest a transition to the family of seals 

 with true single-rooted molars ; the formula 



of this genus is, i. =, c . 



p. 



22 



: = 34". 



22' 1 ' 11 

 The four middle upper in 



2 _ 2 



cisors are close set, with pointed recurved 

 crowns ; the lateral ones are much larger and 

 laniariform : the canines have moderate crowns, 

 with a sharp ridge before and behind. The* 



3 N 2 



