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 

 concave, 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 C7Ti3L7S3Cy2o-23- 



The cervical vertebrae are relativel3r longer than in the ox and the pig. The 

 bodies of the typical vertebree diminish in length from first to last and are com- 

 pressed dorso-ventrally. The anterior extremity is moderately convex and the 

 posterior slightljr 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 

 readilj' distinguished bj' its shortn(\ss, 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 the' 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 bf 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 



