286 Bulletin American Museum of Natural History. [Vol. XXVII, 



"Marsupial" Characters in the Insectivora. 



In the preceding pages we have noted a great many important characters 

 (especially in the general architecture of the skull and in the arrangement of 

 many of the cranial foramina) which are common on the one hand to all 

 Marsupials and on the other to primitive Placentals of widely different orders 

 (pp. 218, 253, 279), so that there is very strong evidence of the former 

 existence of an ancestral Marsupio-Placental stock. The so-called Marsupial 

 characters of Insectivores have been regarded as a direct heritage from this 

 Marsupio-Placental stock, but in view of the widespread tendency for deriv- 

 atives of a common stock to accjuire similar characters after they have become 

 separated from it and from each other, it seems not imj^ossible that certain 

 "Marsupial" characters of various Insectivores may have been acquired 

 independently within the limits of the several modern families. 



Such so called "Marsupial" characters are often variable in the different 

 species and sometimes appear to be related to particular adaptive or cae- 

 notelic requirements. Under this category may be mentioned the following: 



(1) Palatal vacuitie.'i: apparently secondary in the Erinaceoidea (p. 261) 



and Zalambdodonta (p. 254). Absent in Ptilocercus, barely indi- 

 cated in Twpaia, very large in Macroscelides. 



(2) Pronounced post palatal transverse crest: apparently secondary in Erina- 



ceoidea (p. 261) and possibly also in Zalambdodonta; absent in Tu- 

 paia, moderate in Ptilocercus and Macroscelides. 



(3) Tijvipanic wing of aUsphenoid} Only in Ptilocercus and the embryo 



Rhynchocjion does it at all approach the characteristic Marsupial 

 condition and form a concave shell; in the Lipotypla it primitively 

 forms merely a straight ridge separating the tympanic fossa from the 

 glenoid region. 



(4) Optic foramen not separated from the sphenorbital fissure. Confluent 



Avith it in Microgale, Sorex, certain Talpidse, Macroscelides, Rhyncho- 

 cijon. Intermediate conditions in certain Talpidte (Dobson), Tupaia. 

 Well separated in Erinaceoidea, most Zalambdodonts, Ptilocercus. 



(5) Branch of entocarotid perforating basisphenoid: in Erinaceus (at least 



occasionally), Centetes (but c/. also Vespertilionidje, Orycteropus, 

 Herpestinte; van Kampen, 1905, p. 383). Enters through foramen 

 lacerurp medium in Sorex (van Kampen, 1905, p. 435). 



(6) A fourth upper molar: occurring exceptionally in Centetes {cf. Otocyon). 



(7) Vomer ivith large postero -lateral wings: Solenodon, Rhynchocyon. 



(8) Malar extending back to glenoid fossa: Macroscelides (probably second- 



ary). 



1 See also p. 329. 



