330 Bulletin American Museum of Natural History. [\"ol. XXVII, 



expanded into a finally enormous fenestra. The apparent ecfopterygoid 

 fossce, according to Weber (1904, p. 474), in most instances are formed 

 by the spreading of the pterygoids, which often end in backwardly projecting 

 hamular processes. But in the young Lepus these fossfe seem to be normal 

 and comparable with those in Erinaceus, Hyrax, etc., ?'. c., bounded 

 internally by the pterygoids and externally by the pterygoid wings of the 

 alisphenoid. They lodge the large ectopterygoid muscles, which sometimes 

 {e. g., Hystrix), as in Erinaceus algirus, etc. (p. 287) cause the angle to be 

 sharply inflected. 



Relationship of Rodents to Insectivores. — The Rodents appear to approach 

 somewhat more closely toward the Insectivores than toward any other of 

 the typical Placental orders. They are more primitive than the Insectivora 

 in the possession of a completely double uterus, of a uniformly large yolk 

 sack, and sometimes of an accessory yolk sack placenta (Lee, 1908, p. 918), 

 and of the dorso-lumbar vertebral formula of D 13 + L 6 = 19, which only 

 rises to 23 and 25 in very specialized types; whereas in Insectivora only 

 Tiipaia, Solenodon and the Talpidi3e retain the lower number, while in all 

 the others it varies from 20 to 24. On the other hand, in the conditions of 

 the testes the Rodents are somewhat more advanced than the most primitive 

 Insectivores; because the testes do not retain their primitive position but 

 descend at least partially and to a varying extent, in some cases even into a 

 scrotum. 



The ethmoid complex, according to Paulli (quoted by Weber, 1904, p. 474) 

 closely resembles the Insectivore type, i. e., there are four endoturbinals 

 ^\■ith five scrolls, and a very large naso-turbinal. The ossicula auditus are 

 extremely variable in form in different families. The malleus in the Myo- 

 morpha has a broad lamina and an orbicular apophysis as in Shrews and 

 Bats (Doran, 1879, pp. 410, 418). The Jacobson's organ of Rodents is of 

 a very peculiar type (Broom, 1898). In the more primitive forms the manus 

 and pes, as in Insectivora is characterised by the subequality and symmetrical 

 arrangement of digits II, III and IV, digit III being somewhat the longest. 

 The carpus frequently retains a free centrale and primitively a well defined 

 lunar-unciform contact. Fusions of the scaphoid and lunar, of the tibia 

 and fibula, occur in both Rodents and Insectivores. The radial, ulnar and 

 tibial sesamoids, which occur also among the Insectivora, are developed to a 

 high degree in various Rodents, sometimes simulating the digits in becom- 

 ing jointed and provided with a claw-like structure. The names " prjepoUex," 

 "postminimus," and "pra4iallux" have been applied to these structures, 

 but Weber (1904, p. 476) regards them not as true digits but as pure sesa- 

 moids. x\t any rate they seem to be very ancient structures since they are 

 foreshadowed in the manus of the Permian Theriodesmus (p. 440). The 



