374 NOTES ON THE CANID.E OF THE WHITE RIVER OLIGOCENE. 



III. The Brain (PI. XIX, Fig. 12). 



The brain of Cynodictis has already been described by Bruce ('83, p. 41), but as I 

 wish to consider it from a different standpoint, some account of it will be necessary. In 

 this genus the brain is relatively smaller than in any of the recent Canidce. The olfac- 

 tory lobes are large and are left exposed by the hemispheres, with which they are con- 

 nected by short and thick olfactory tracts. The cerebral hemispheres are pear-shaped, 

 broad behind, but tapering rapidly forward, where they decrease in vertical as much as 

 in transverse diameter. The frontal lobe is short, narrow and of small vertical depth, 

 while the parietal lobe much surpasses it in every dimension ; a transverse depression 

 marks the boundary between the two. The temporo-sphenoidal lobe is also quite well 

 developed and adds materially to the dorso-ventral diameter of the brain in this region. 

 Posteriori)- the hemispheres slightly overlap the lateral lobes of the cerebellum (which 

 appears not to be the case in Dap7iamus), but leave the vermis entirely uncovered. The 

 shape of the cerebrum is thus alopecoid rather than thooid in character. In the former 

 scries the hemispheres are wide behind and taper anteriorly, with slight incurvations at 

 the sylvian and presylvian fissures, while in the thooids the cerebrum is narrower behind 

 and at the presvlvian fissure the sides are abruptly incurved almost at a right angle ; 

 the frontal lobes are much larger relatively than in the foxes (see Huxley, '80, pp. 245- 

 247). The hemispheres of Cynodictis agree well in shape with those of the alopecoids, 

 and when compared with the brain of the later and more advanced genus Cynodesmus 

 from the John Day, the greater width of their posterior region is distinctly to be seen. 

 The whole character of the skull makes it evident that Cynodesmus is a thooid, while 

 both brain and skull structure approximate Cynodictis more to the alopecoids. 



The hemispheres are very simply convoluted and the sulci are few, simple and short, 

 though it should not be forgotten that the brain-cast very probably fails to reproduce all 

 of the fissures. In the recent Canidce the convolutions are numerous and complex, and 

 the sulci pursue a remarkably curved course, giving to the convolutions, when seen from 

 the side, the appearance of a succession of U-shaped, concentric coils, grouped around 

 the sylvian fissure as a centre. In Cynodictis, on the other hand, the visible sulci are 

 few, shallow, short and nearly straight. On the dorsal surface of the hemisphere only 

 two fissures arc to be observed, the lateral and the suprasylvian, the former of which is 

 short and almost straight, dying away before it reaches the hinder part of the parietal 

 lobe. If the coronal sulcus is present at all, it is in the same fore-and-aft line as the 

 lateral, and has not the outward sweep around the crucial fissure which is so characteris- 

 tic of Canis. No trace of the crucial fissure is preserved in the brain-cast, and if it was 

 present in the brain, it must have been short, as is indicated by the straight course of the 



