46 ELEMENTS OF MAMMALIAN ANATOMY. 
trad or ventromediad; a body whose transverse diameter is 
greater than the vertical diameter; and transverse processes. 
There are two half facets on each side of the body of every 
thoracic vertebra except the first, eleventh, twelfth, and 
thirteenth. The head of a rib thus articulates with two 
vertebre (Fig. 28). The body of the first vertebra bears 
on each side a whole facet and a half facet. The eleventh, 
twelfth, and thirteenth bear a whole facet on each side of 
the body. 
The transverse processes of the first eleven bear facets 
for the articulation with the tubercles (Fig. 25) of the 
ribs. The last three thoracic vertebre are characterized by 
mammnillary processes springing from the dorsolateral por- 
tion of the roots of the anterior processes. 
The following features are common to all of the lumbar 
vertebre: a spinous process projecting dorsocraniad (Fig. 
26); a transverse process projecting ventrocraniad on either 
side from the body; anterior articular processes and poste- 
rior articular processes. A mammillary process is present 
on the root of the anterior articular process of the first five 
bones, and an accessory process occurs on the caudal margin 
of the wall of the neural arch of all except the last vertebra. 
The transverse processes increase in length and curvature 
caudally. The spinous processes increase in length in the 
same order, and the neural canal likewise enlarges caudally. 
The sacrum is a single bone (Fig. 27) formed by the 
union of three sacral vertebre. The limit of each element 
is marked by the dorsal and ventral intervertebral foramina 
which furnish passage for the dorsal and ventral branches 
of the spinal nerves. The two tubercles on either side of 
each of the three median spinous processes are the result 
of the fusion of the articular processes. The cranial por- 
tion of the bone presents on its lateral aspect the auricular 
