188 SKELETON OF THE DOG 
duced in size. The transverse processes of the first five or six are relatively large; 
behind this they quickly disappear. -Hemal arches (or chevron bones) in the form 
of a V or Y occur ventrally at the intercentral junctions of the third, fourth, and 
fifth usually. They transmit the middle coecygeal artery, which passes between 
pairs of ventral tubercles further back. 
Curves.—A gentle curve, convex ventrally, is formed by the cervical and the 
anterior part of the thoracic region. The posterior thoracic and the lumbar 
vertebrae form a second curve, concave ventrally. The sacral promontory is well 
marked. The sacrum and the anterior part of the coccygeal region constitute 
a third and more pronounced curve, concave ventrally. In long-tailed dogs the 
sacro-coceygeal region is somewhat S-shaped. 
Variations.—Numerical variations are not common except in the coceygeal region. The 
number of thoracic vertebrae may be twelve or fourteen, with or without compensatory change in 
the lumbar region. Girard recorded a case with eight lumbar and the usual number of thoracic 
vertebrie. Six lumbar with fourteen thoracic vertebra have been met with. The first coceygeal 
sometimes unites with the sacrum. 
THE RIBS 
Thirteen pairs of ribs are present, of which nine are sternal and four asternal. 
They are strongly curved, narrow, and thick. Those in the middle of the series 
are the longest. The first eight or nine increase in width in their lower part. The 
last rib is usually floating. The costal cartilages are long and curve ventrally and 
forward; the length and curvature of the first pair are striking special features. 
THE STERNUM 
This is long, laterally compressed, and consists of eight sternebree, which fuse 
only in exceptional cases and in extreme old age. The first segment is the longest; 
its anterior end is blunt-pointed and bears a short conical cartilage. It widens 
at the point of articulation of the first pair of cartilages. The last segment is 
also long, thinner than its predecessors, wide in front, and narrow behind, where it 
bears a narrow xiphoid cartilage. 
The thorax is distinctly barrel-like and is not decidedly compressed anteriorly 
like that of the horse and ox. The inlet is oval and is relatively wide on account 
of the marked curvature of the first pair of ribs and cartilages. 
BONES OF THE SKULL! 
CRANIUM 
The occipital bone is similar in position to that of the horse. The nuchal crest 
is prominent, angular, and directed backward. Just below the crest are two rough 
imprints or tubercles for muscular attachment. The surface below these is convex 
from side to side and concave dorso-ventrally. On each side, at the junction 
with the squamous temporal, is the mastoid foramen which opens into the cranial 
ravity. The condyles are somewhat flattened and are widely separated above; 
at the medial side of each is a short condyloid canal, which opens into the temporal 
‘anal. The paramastoid processes are very short. The basilar part is wide and 
joins the bulla ossea on either side; its ventral surface is flattened and the tubercles 
are at the junction with the bulla. The hypoglossal foramen is small and is close 
to the foramen lacerum posterius; the latter is bounded in front by the bulla ossea, 
behind and medially by the occipital bone. 
‘In the following descriptions of the separate bones an intermediace type—e. g., a fox terrier, 
—is selected, and the most striking differences in the brachycephalic and dolichocephalic breeds 
will be considered in the section on the skull as a whole. 
