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



the alisphenoid (Parker, /. c, p. 271). In the Placentals, in consequence of 

 the early development of the large lateral masses of the cerebrum, the wall 

 of the chondrocranium is "ruptured" (/. c, p. 8) and the ala temporalis 

 (aUsphenoid) appears as a projecting wing of cartilage. 



(2) Cartilaginous nostrils subterminal and giving off tongue-shaped 

 cartilages which cooperate with the " antero-lateral vomers" (prevomers) to 

 protect Jacobson's organs. 



(3) Whole nasal labyrinth small especially in the young, "not more 

 than half as large as in an average Placental ^lammal" (/. c, p. 271); but 

 nasal labyrinth much more complex than in any reptile (/. c, p. 8). Cribri- 

 form plates suberect, flatfish (/. c, p. 272). 



(4) Meatus externus protected by a more or less segmented tube of 

 cartilage, which is continuous with the concha auris (/. c, p. 270). (Indi- 

 cates that the cartilages of the ear conch are neomorphs in the mammals, 

 and not necessarily derived from the hyoid arch (c/. p. 125)). 



(5) Presphenoid (/. c, p. 271) developing as an independent cartilage. 

 (In Placentals it generally appears as a ventral union of the orbitosphenoids.) 



(6) Optic nerve (/. c.) not piercing the cartilaginous orbitosphenoid, 

 but, from its first a])pearance, issuing through the sphenoidal fissure, as in 

 reptiles. (Contrast most Placentals.) 



(7) Internal carotid piercing basisphenoid (r;/'. ]\Ionotremata; p. 150). 

 (In Placentals it generally enters through the foramen lacerum medium, 

 pp. 430, 431). 



(8) Clinoid processes and concavity for the pituitary body but little 

 developed {cf. Solenodon, p. 253). 



The arrangement of the eranial foramina in Marsupiah'. 



Strong evidence for the common origin of the Polyprotodont and Diproto- 

 dont divisions of the Marsupialia lies not only in the structure of the feet 

 (pp. 201, 217) but more especially in the common plan of arrangement of 

 the cranial foramina and of the parts relating to audition, in such adaptive ly 

 diverse forms as Marmosa, Didelphis, Phascologale, Dasyurus, Thylacynus, 

 PerameJes, of the Polyprotodontia; Caenolestes, Phalangista, Phascolarctos, 

 Hypsiprymnus, Macropus and Phascolomys of the Diprotodontia. Repre- 

 sentatives of all these genera have been examined by the Avriter, with the 

 cooperation of several fellow students especially Dr. C. S. Mead. 



The majority of the foramina mentioned above as occurring in the 

 Didelphids are equally characteristic of other JNIarsupials. The optic 

 foravien -(as is well known) is not independent but is confluent with the 

 foramen lacerum anterius (sphenorbitale), which also transmits nerves 



