SINUS PARANASALES EARLY TERTIARY MAMMALS 141 



These sinuses occupied the entire cavity of the maxillary bone, 

 as in the sheep, and projected posteriorly into the zygomatic 

 arch, to a point below the orbit. The maxillary sinuses are not 

 so many nor so complex as in the sheep, but the posterior divi- 

 sion of the inferior group extends much further into the zygo- 

 matic arch. There are several minor sacculations of the sinus 

 maxillaris inferior, one below the horn-like projection, Anteri- 

 orly there is a rather large accessory sinus. Leading backward 

 from this cavity is a canal which is possibly homologous to the 

 ostium accessorium of human anatomy. The accessory sinus 

 is not very prominent laterally, but has a large expanse antero- 

 posteriorly, extending beyond the premaxillo-maxillary suture. 



The two canals, which have been designated ostium maxillare 

 and ostium accessorium, connect the two great divisions of the 

 sinus maxillaris (inferior and superior) with the sinus frontalis, 

 and for this reason I have supposed they have been properly 

 designated. The surfaces of all the casts are richly supplied 

 with blood vessels. 



The brain cast (fig. 2) is very similar to that of the sheep, 

 with which it has been compared in naming the gyri and sulci. 

 The various divisions of the encephalon will be fully described 

 later. 



The other cast (fig. 5) is that of a bear-dog (Daphaenus) from 

 the White River Oligocene of South Dakota. This cast is not 

 so well preserved as the oreodont, and not so much detail can 

 be discerned, but sufficient is present to warrant a description. 

 In order that the nature of the species may be understood, it 

 will be necessary to say that Daphaenus felinus is the ancestral 

 form of a group of bear-dogs, members of the family Canidae, 

 which appeared in well-developed form in North America during 

 the Oligocene and Miocene times. Their ancestors are prob- 

 ably to be found in the Creodont family, the Miacidae, of the 

 Uinta Eocene. 



Through the Oligocene the phylum (Canidae) was carried back by 

 the several species of Daphaenus, assuredly the ancestor of Daphaeno- 

 don and decidedly more primitive in many respects. The Oligocene 

 genus was a much smaller animal than its lower Miocene successor, 



