48 THE DOG'S SKULL. 
erooved on their inner and anterior 
surface, and sharper on their posterior 
surface. They are also slightly larger 
than those in the upper jaw. 
ili. The premolars are eight in number. 
They aremore compressed, and sharper, 
than those of the upper jaw. 
iv. Thesmolars: “There pare three pairs 
of molars in the lower jaw. The 
firstis very different from the upper one. 
It is the seetorial tooth of the lower 
jaw. It has four cusps. 
SECTIONS. 
Many points in the structure of the skull, such 
fom, Instance as. the relations of the bones of the 
occipital segment, auditory capsule, nasal cavities, &c., 
are best studied by an examination of a series of 
sections. 
A. Longitudinal Vertical Section slightly to the 
left of the median line (Fig. 7). 
Notice that the skull has a longitudinal central 
axis—the eranio-facial axis—the bones of 
which form the basal region of the skull, and 
support the three segments of the cranial 
region, which form the cranial cavity and 
enclose the brain. This cavity may conveni- 
ently be divided into three compartments, the 
