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 coccygeal 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-coccygeal region is somewhat S-shaped. 



Variations. — Xumerical variations are not common except in the coccygeal region. The 

 number of thoracic vertebra 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 

 vertebrEe. .Six lumbar with fourteen thoracic vertebrae have been met with. The first coccygeal 

 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. I'he 

 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 sternebrse, 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, mde in front, and narrow behind, where it 

 bears a narrow xiphoid cartilage. 



The thorax is distinctly barrel-like and is not decidedlj' 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 SKULLS 



CRANItTM 



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 

 cavitjr. The condjdes are somewhat flattened and are widely separated above; 

 at the medial side of each is a short condyloid canal, which opens into the temporal 

 canal. 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 ^^dth 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 intermediate type — e. g., a fox terrier, 

 — is selected, and the most striking differences in the brachy cephalic and dolichocephalic breeds 

 will be considered in the section on the skull as a whole. 



