184 SKELETON OF THE DOG 
tral and fourth tarsals. The tuber calcis is deeply grooved posteriorly. The 
central tarsal is narrow transversely and thick. Its proximal surface is deeply 
coneave, and the plantar bears a large tubercle. The first tarsal is high and 
narrow; it articulates with the central and second tarsals and the second metatarsal 
bone. The second tarsal is small and somewhat prismatic; it articulates with 
the central above, the third in front, the first behind, and the second and third 
metatarsals below. The third tarsal is much larger, and is compressed from above 
downward, wide in front, narrow behind. It articulates with the central tarsal 
above, the third metatarsal below, the second tarsal medially, and the fourth tarsal 
laterally. The fourth tarsal is large. Its lateral face is crossed by an oblique 
groove for the tendon of the peroneus longus. The medial surface articulates 
with the central and third tarsals. The proximal surface supports the tibial and 
fibular tarsal bones, and the distal surface rests on the fourth and fifth metatarsals. 
It ossifies from two centers. The summit of the tuber calcis fuses with the rest 
of the bone at two to two and a half years. 
The four metatarsal bones resemble the corresponding bones of the fore limb, 
but are somewhat longer. The proximal ends of the third and fourth each have a 
considerable plantar projection; the process on the third has a facet for articulation 
with a discoid sesamoid bone. The second and fifth are placed more toward the 
plantar aspect of the large bones than is the case in the fore limb. 
The first and second phalanges are a little longer and narrower than those of 
the fore limb. 
SKELETON OF THE DOG 
VERTEBRAL COLUMN 
The vertebral formula is C7T13 L753Cy20-23. 
The cervical vertebre are relatively longer than in the ox and the pig. The 
bodies of the typical vertebrae diminish in length from first to last and are com- 
pressed dorso-ventrally. The anterior extremity is moderately convex and the 
posterior slightly concave; both are oblique. The median ridge and lateral grooves 
on the dorsal surface of the body are very well marked. The second, third, and 
fourth have distinct ventral spines. The spinous process of the third has the 
form of a long low crest; in the remainder it is higher, blunt-pointed, and inclined 
forward. The transverse processes of the third, fourth, and fifth project ventrally 
and backward, and divide into two branches; of these, the anterior one is thin, 
and the posterior is thick and tuberculate at its free end. The process of the 
sixth has two parts; one of these is an extensive quadrilateral plate which is di- 
rected ventro-laterally and is ridged on its medial surface; the other part is short and 
blunt, and is directed outward and a little backward and upward. The seventh is 
readily distinguished by its shortness, the length of its spine, and the single trans- 
verse process. The posterior articular processes bear tubercles which are large on 
the third, fourth, and fifth. 
The ventral arch of the atlas is narrow from before backward, and bears a 
small tubercle posteriorly. The dorsal surface of ther dorsal arch is strongly convex 
and rough centrally. The wings are wide, flattened, and almost horizontal. The 
dorsal surface is rough. There is an alar notch (Incisura alaris) on the anterior 
border instead of the alar foramen. The foramen transversarium is present. 
The body of the axis is flattened dorso-ventrally, especially in front. The 
dens is rounded and relatively long, reaching almost to the occipital bone; it is 
inclined upward a little. The articular surfaces which flank it are condyloid in 
form and very oblique. The ventral surface is wide, and is divided by a median 
