THE RIBS — THE STERNUM — BONES OF THE SKULL 



153 



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. — Numerical variations are not common except in the coccygeal 

 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 vertebrae. Six lumbar with fourteen 

 thoracic yertebrse 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. 



Th(\v 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. 





-^ 



Fio. 120. — Fourth Lumbar Vertebra of Dot;, Lkft 

 View. 

 a, b, Articular surfaces of body; c, transverse 

 process; d, accessory process; e, anterior articular pro- 

 cess; e', man^millary process; /, posterior articular pro- 

 cess; g, spinous process. (EUenberger-Baum, Anat. d. 

 Hundes.) 



Fig. 121. — Sacrum of Dog, Dorsal View. 



a. Dorsal sacral foramina; b, articular surface 

 of body of first segment; c, d, anterior articular pro- 

 cesses; e, wing; /, rudiments of articular processes; 

 g, lateral part; /;, spinous processes. (Ellenberger- 

 Baum, Anat. d. Hundes.) 



The costal cartilages are long and curve forward; the length and curvature of 

 the first pair is a striking special feature. 



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, wide in front, and narrow behind, where it 

 bears a narroAv xiphoid cartilage. 



The thorax is distinctly barrel-like and is not decidedly compressed anteriorly 

 hke 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 



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 brachycephalic and dolichocephalic breeds 

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



