February 19, 1897.] 



SCmNGE. 



291 



adults. This is caused by ossification of 

 the stylo-hyoid ligament, which is often 

 represented by a separate bone in lower 

 animals. 



The domestic cat exhibits, as a rule, no 

 tubercle on the lachrymal bone. In the 

 senile skull of this species the tubercle is 

 present. It is of interest to note that 

 among the following skulls of Felis in the 

 Academy of Natural Sciences, Philadelphia, 

 and the National Museum, Washington, 

 four only (^F. eyra and F. yaguarundi, F. 

 catus and F. caracal) exhibited the lachrymal 

 bone as it is in the vigorous adult of F. 

 domesticus. In the following species the 

 tubercle was present, though small : F. 

 pardus,* F. rufus, F. canadensis, F. pardalis,f 

 F. leo. In the following it was large and 

 formed precisely as in the old examples of 

 the domestic cat, F. caligata, F. onca, F. 

 concolor, F. tigris. Thus the form of the 

 lachrymal bone in the old cat reverts to 

 that of the prevalent type, not by absorp- 

 tion, as in Proposition I., but by the crea- 

 tion of a conspicuous process of bone. 



The senile cat again exhibits hyperosto- 

 sis of the lateral process of the frontal bone 

 (post-orbital process) as well as of the as- 

 cending process of the malar bone. Thus 

 these processes approach each other and in- 

 dicate the tendency to union shown in re- 

 lated efficient forms of the clawed mam- 

 mals in which such union actually takes 

 place. 



IV. Both the upper and the loiver jaws of 

 certain mammak tend to elongate in old age. 



The animals already named possessing 

 long jaws have the intervals between some 

 of the premolars widened in senility. The 

 vigorous greyhound has the third lower 

 premolar almost in contact with the fourth, 

 while in the jaw of an old mongrel it is 

 widely separated therefrom. In a general 



*A small tubercle may occur in this species as a 

 variation. 



t Absence of tubercles may be noted as variations. 



way, it may. be said that the last three pre- 

 molars are all more widely separated from 

 one another than in younger individuals. 

 The cause appears to lie in the disposition 

 for the jaw to extend forward somewhere 

 in front of the region of the molar teeth; 

 for the extraordinary wear that sometimes 

 takes place between the lower canine and 

 the upxter outer incisor can be explained in 

 no other way. In an old dog (No. 22,563, 

 U. S. Nat. Mus. ) the lower canine had 

 pressed against the upper second and third 

 incisors and had worn away the teeth. 

 The permanent premolars always lie close 

 together when recently erupted. This dis- 

 position appears to be a corollary to the 

 law of the vertical succession of these teeth. 



The large permanent teeth following the 

 small deciduous teeth in exact infra-posi- 

 tion compel the former to lie close together. 

 But they tend to separate afterward, espe- 

 cially for the first and second to separate 

 from the third and fourth. In the domestic 

 cat the interval between the second and 

 third teeth is more variable than between 

 the others. As a rule, it is but 2 mm. in 

 front of the third tooth, though it may be 

 as much as 5 mm. These proportions are 

 maintained throughout life in this species, 

 so far as I know. 



In the dog we have a much greater va- 

 riety, since in the different breeds the face 

 axis is modified. In the short-faced types 

 the premolars retain their early crowded 

 condition, or this may even be exaggerated; 

 while in the long-faced types they tend to 

 be separated, excepting the third and fourth 

 teeth, which remain, at least in an exam- 

 ple of the greyhound above noted, close 

 together. 



Putting aside the pug dogs and bull dogs, 

 the variations in the intervals between the 

 premolars are marked and appear to be inde- 

 pendent of the relative length of the face to 

 the brain case. In the St. Bernard the 

 first lower premolar (counting it as a re- 



