1010.] Zciiglodonts; Cdncca net of Mesozoic On'(;iii. 419 



for the temporal, and weak attachments for the masseter muscles in Zeuglo- 

 don also favor this view. 



(3) No Creodonts are known in which the petrotym})anic bullae are 

 expanded as they are in Protocetus. This however is an aquatic adaptation 

 seen also in the Pinnipedia, and like the backward prolongation of the 

 palate (which is a point of resemblance to the Creodont Hyaenodon) it may 

 be of little phylogenetic significance. 



(4) The marked post-orbital constriction is no necessary indication of 

 Creodont affinity. In the Seals and probably in Protocetus this is largely 

 secondary and due apparently to the reduction of the olfactory parts of the 

 brain. In the Creodonts themselves it is due not to any actual narrowing 

 but to the very rapid broadening of the muzzle and zygomata in adaptation 

 to carnivorous habits. In all three cases it is readily derivable (p. 267) from 

 the tubular postorbital region represented in the Zalambdodont Microgale. 



(5) It is a very surprising fact that the skull of the little Zalambdodont 

 genus Hemicentetes presents a superficial analogy to that of the Zeuglodonts 

 in a number of points, such as the great elongation of the muzzle, the low 

 anterior position of the orbits, the shape of the lower jaw, etc., and in the 

 cheek teeth the reduction of the inner ])art of the crown and the elonsation 

 of the outer ])art. Together with the marked aquatic modifications of the 

 limbs in the Eocene Panto/e.stes, these curious resemblances indicate that the 

 Insectivora did occasionally develop features Avhich might be thought at 

 first to be entirely distinctive of the Zeuglodontia. 



(6) The true molars of Protocetus present only a superficial resemblance 

 to those of any Hyjenodont. The reduction of the inner side of the molar 

 crown has been effected independently also in the Pinnipedia and, as stated 

 above, in Hemicentetes. The relatively small size of the canine and the very 

 large size of the third premolar also tend to remove Protocetus from the Creo- 

 donts. 



Tlie Cetacea not of Mesozoic origin. Evidence in contradiction of the 

 view that the Cetacea are an extremely ancient (?'. c., Mesozoic) branch of 

 the Mammalia is furnished by the reproductive organs. The reproductive 

 organs seem to have been affected relatively little by the process of adapta- 

 tion for aquatic life which has so profoundly changed the entire skeleton 

 and the digestive, respiratory and vascular systems. The uterus is two 

 horned, as in many Monodelphia of high type {e. g., Carnivora, Artiodactyla, 

 Perissodactyla), the yolk sack is rudimentary (contrast most primitive 

 Placentals). The penis (in contrast with that of Rodents and Edentates) 

 is also of high type (Weber, 1909, p. 571). 



In the highly convoluted brain (see Weber, 1909, pp. 126, 562) the three 

 concentric gyri which surround the Sylvian fissure are characteristic of i\\v 



