THE SKULL AS A WHOLE 195 
its length and is a little everted, especially in its middle; it presents seven alveoli 
for the lower cheek teeth, which resemble those of the upper jaw except that the 
fourth and sixth are much smaller and the fifth is like the fourth of the upper series. 
The interalveolar space is very short or even absent. There are two or three men- 
tal foramina on either side. The vertical part is relatively small. Its lateral sur- 
face presents a deep masseteric fossa (Fossa masseterica) which encroaches on the 
coronoid process and is limited by ridges in front and below. The medial surface 
is convex and is marked by the usual mandibular foramen. At about the same 
level as the latter is the rough angular process (Processus angularis), which pro- 
jects backward from the posterior border, and is equivalent to the angle of the 
other animals. The condyle is placed very low—not much higher than the apex 
of the canine tooth when the bone is resting on a flat surface. It is long trans- 
versely and the medial part of the articular surface is much the wider and extends 
over the posterior surface. Its long axis is a little oblique, the medial end being 
inclined somewhat downward and forward. The coronoid process is very exten- 
sive and is bent slightly outward and backward. 
The body of the hyoid bone is a slightly curved transverse rod; it is compressed 
from before backward, and bears no lingual process. The thyroid cornua are per- 
manently attached to the body by cartilage; they diverge widely, curve inward, and 
are compressed laterally. The small cornua are short, prismatic, and strong. The 
middle cornua are commonly a little longer than the great cornua; they are com- 
pressed laterally, and are slightly enlarged at the ends, which are joined by cartilage 
to the adjacent cornua. The great cornua are bent outward and are somewhat 
twisted. 
THE SKULL AS A WHOLE 
The different breeds of dogs display great variations in the form and size of 
the skull. Those which have a long narrow skull (e. g., greyhound, collie) are 
designated dolichocephalic. Other dogs (e. g., bulldog, small spaniels, pugs) have 
very broad, short skulls and are termed brachycephalic. Intermediate forms 
(e. g., fox terrier, dachshund) are mesaticephalic. 
The length is usually measured from the nuchal crest to the anterior end of the premaxil- 
lary suture, and the breadth between the summits of the zygomatic arches. The cephalic index 
is the relation of the breadth to the length, assuming the latter equal 100; the formula is: 
breadth < 100 
length 
as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in the pug and 
some toy terriers. Among the mesaticephalic types are the fox terrier, with an index of about 
70, and the white Pomeranian, with one about 72 to 75. The cranio-facial index is the relation of 
the distance between the nuchal crest and the fronto-nasal suture to that between the latter and 
the nasal notch. It varies from 10 : 3 in extreme brachycephalic breeds to 10 : 7 in extreme 
dolichocephalic subjects. 
= cephalic index. The index of extreme dolichocephalic breeds is about 50, 
The frontal surface shows the wide outward curve of the zygomatic garches 
and the great extent of the temporal fossze. The latter are separated by the parietal 
crest, which in the larger breeds is very strong and prominent, and is continued by 
the diverging frontal crests to the supraorbital processes. The frontal and nasal 
regions are centrally depressed, and are more or less concave in profile. The nasal 
region is narrow and is terminated in front by a nasal notch. In the extreme 
brachycephalic breeds the differences are very striking. The cranium is strongly 
convex in both directions and is considerably longer than the face. The parietal 
crest is more or less effaced posteriorly and is formed by the interparietal only. The 
parietofrontal crests are separated by an interval behind and diverge to the supra- 
orbital processes, so that the temporal fossze are widely separated. The frontal 
region is wide, strongly convex, and has a shallow central depression. The nasal 
region is very short, relatively wide, and centrally depressed. In profile there is a 
