178 
marked influence upon the conformation of the basis cranil. As 
no attempt has been made to describe this part of the skull in 
Notoryctes, it may be of interest to add brief notes of what could 
be made out in a “ wet” specimen. 
A comparison of the brain and cranium in the Proto- and 
Meta-theria affords a number of instances of the mutual moulding 
influence of these two parts upon one another. Thus in Echidna 
the cranial cavity is very short—possibly for phlyogenetic or 
functional reasons—and offers a restraining influence upon the 
pallium as it tends to increase in the sagittal direction. <As a 
consequence the pallium becomes convoluted mainly in a trans- 
verse direction, so that, with the bending of the hemisphere, its 
fissures have a radiating arrangement. In the higher Metatheria 
the elongated form of the cranium allows a greater sagittal ex- 
tension of the cerebrum, so that the transverse or radiating folding 
of Echidna is not found in Marsupials; but in all the higher 
forms there is a long narrow, somewhat pointed frontal pole— 
Macropus, Thylacinus, Thylaceo (Gervais, 14). These are 
examples of cerebral folds directly resulting from the restraining 
influence of the cranial wall upon the growing pallium. In the 
case of the tuberculum olfactorium and olfactory bulb it is clearly 
demonstrated how that local conditions of over-growth—localised 
hypertrophy of certain regions—can produce irregularities in the 
brain surface, which mould the growing brain-case and determine 
to a large extent its shape. 
The united basi-occipital and basi-sphenoid mass forms a rela- 
tively broad, gradual slope, which extends from the foramen 
magnum upwards and forwards as far as the foramina lacera 
antica. This sloping surface is perforated on either side of the 
middle line at about the middle of the basisphenoid by the carotid 
foramen. Between these foramina the pituitary body rests upon 
the basisphenoid, roofed over by a thin fold of dura mater. Dr. 
Stirling, who described (38) such of the inner aspect of the 
cranium as could be seen through the foramen magnum, says that 
the floor ‘‘rises in front of the basisphenoid region into a well- 
marked eminence, which slopes away on either side. Anterior 
to this again the floor is flat.” The anterior flat area is the broad 
cribriform plate of the ethmoid. In the middle line this is con- 
tinued backwards into the well-marked eminence, which appears 
to be formed by the meeting of the orbito-sphenoids. . On either 
side of this ridge, and behind the cribriform plate, the floor 
rapidly slopes away into a well-marked hollow, which lodges the 
tuberculum olfactorium. The posterior part of this hollow is 
formed by the alisphenoids, whilst laterally it extends well on to 
the lateral cranial wall, where the parietal takes a share in its 
formation. Mesially it extends as far as the basisphenoid. 
