1004 
Journal of Agricultural Research 
Vol. XXVIII, No. 10 
There is much variation in the precise angle and the amount of projection of 
the zygomatic root of this bone. The greatest degree is, of course, met with in 
the case of individuals with maximum zygomatic width, and in these the angle is 
less acute. As previously mentioned, the zygomatic width is greatest in skulls 
that are most heavily ridged, and in such the postorbital processes of the squa- 
mosals are also somewhat better developed and more angular, the prominence 
of the latter depending directly upon the development of the deep portion of the 
temporal muscle. In animals with greatest development of this character the 
lateral slope of the anterior border of the braincase is most abrupt and squarish. 
In the case of heavily ridged and angular skulls the pull exerted by the powerful 
superficial part of the temporal muscles from their attachments upon the temporal 
ridges has actually flattened out the underlying portion of the squamosals between 
the ridges and the zygomatic processes, making them flatter than is the case in 
weaker skulls. Thus the temporal ridges, instead of being true ridges such as 
often occur in the interorbital region, are in reality the apices of angles formed 
by the superior and lateral surfaces of the cranium. 
Mastoids. —The mastoid is very irregular in outline and closely embraces the 
audital bulla supero-medially. In the articulated skull it occupies the space on 
either side between the lambdoidal process, being bounded supero-medially by 
the exoccipital. The anterior portion, embracing the audital bulla, is visible 
within the prelambdoidal fenestrum and along the premastoid vacuity. The 
visible portion is quite variable, depending directly, upon analogous differences in 
the adjoining border of the occipital. 
Audital bullae. —Each one of these globular bones seems to form a true 
suture only with the mastoid, although there are false sutures connecting it more 
or less securely with the basi- and alisphenoids, squamosal, and basioccipital. 
Variation in the audital bulla is not of such a nature as to be measured readily, 
and one should be cautious in making statements regarding variations of an 
intangible sort. There is slight variation with age, the greatest being in the 
width of the anterior portion, and the whole being perhaps more globular in 
juveniles. There is little individual, proportionate variation, although a few 
specimens do have bullae that are slightly more globular than the average. It 
is in the relative size, or mass, that the chief difference lies. Upon the whole, 
this is of a sufficient amount so that it must be taken into consideration, but is 
not excessive. The auditory meatus varies but slightly in shape and size. In 
adult skulls, however, the antero-superior border projects laterally to a con¬ 
siderably greater extent than is the case with juveniles. 
Sphenoids. —The articulations between the sphenoid bones are not always 
to be distinguished without difficulty in skulls of such small size. The ali- 
sphenoid articulates with the squamosal, frontal, maxilla, and the other sphen¬ 
oids. Superiorly the suture formed by its connection with the squamosal ex¬ 
tends forward from a point barely inferior to the premastoid vacuity to its junc¬ 
tion with the frontal at a point slightly antero-medial to the postorbital process; 
thence it descends along the frontal to the orbitosphenoid and the sphenoidal 
fissure. From the latter the maxillary-alisphenoid suture extends obliquely 
rearward to join the external pterygoid plate immediately posterior to the third 
molar. The alisphenoid constitutes the entire lateral surface of this plate and 
the posterior portion of its medial surface, as well as the posterior portion of 
the floor of the pterygoid fossa. Although there are, of course, many differences 
in the precise configuration of this bone, these are relatively slight in degree. 
The most apparent difference occurs in animals of the two extremes of age through 
the lengthening of the pterygoid region as the animal grows, with consequent 
