ENDOCRANIAL ANATOMY OF FOSSIL MAMMALS 363 
olfactory trigone until it disappears in the broad sylvian depres- 
sion (fig. 14). The rhinal fissure is suggested by a shallow 
depression inferior and parallel to the posterior limb of the 
orbital sulcus. 
This brain on the whole is even more advanced in its cerebral 
complexity than many of the modern Cynoidea. The gyri are 
more complex, with more frequent modifications than is seen 
even in the domestic dog. Perhaps the cerebral complexity of a 
wild animal is to be correlated with its incessant necessity for 
self-preservation—an instinct more or less dormant in domestic 
animals. It is also possibly true that there is no adequate 
explanation of such cerebral complexity. This being exhibited in 
one branch of the rodents and absent in another group would 
indicate something of the puzzling nature of this problem. 
The base of the brain is well shown in figure 15, and its features 
are so clearly represented there that a detailed explanation of its 
anatomy will not be given. It is, of course, understood that the 
elevations labeled as cranial nerves are casts of the foramina 
through which the nerves coursed. The pituitary elevation is 
seen posterior to the internal carotid artery. 
The cerebellar fossa of Aenocyon is not so clearly marked as 
is the cerebral, hence a cast of the fossa does not give quite so 
good an idea of the endocranial anatomy as one would desire. 
The form of the lobus anterior is partly hidden by the over- 
hanging cerebrum, and I am unable to locate the sulcus primarius. 
There is a prominent portion which I take to represent the lobulus 
simplex. The lobulus paramedianus lies close to the lobus pos- 
terior, much as in the modern dog, and it is about as slender. 
There is a well-developed lobulus petrosus and all subdivisions 
have indications of lamellae, thus indicating a modern cynoid 
development in this region. 
The artificial endocranial cast of Aenocyon dirus has the fol- 
lowing measurements: 
Length of entire (cast as Mme ty kei jy te eas «opus iitiv socetete aoe 95 
Greatest len gin Of GCerOUxmi eee et. kk oe awh cote eee 70 
Greatest: widthiof (cerebrum: S420). 08. 9)0 esse: BS ER Zins 0 MA ey 65 
erigth.of olfactory bulb... Aeage A ehieos weds oat d. Ge ac. alld 15 
Mad nO olbaetary. bulla, osc ae as tices 3 crc re eee ene oF ween 16 
