THE SKULL AS A WHOLE 159 



it presents seven alveoli for the lower cheek teeth, which resemble those of the 

 upper jaw except that the fourth and sixth are much smaller and the fifth is like 

 the fourth of the upper series. The interalveolar space is very short or even absent. 

 There are two or three mental foramina on either side. The vertical part is 

 relatively small. Its external surface presents a deep masseteric fossa which 

 encroaches on the coronoid process and is limited by ridges in front and below. 

 The internal surface is convex and is marked by the usual foramen. At about the 

 same level as the latter is the rough angular process (Processus angularis), which 

 projects backward from the posterior border, and is equivalent to the angle of the 

 other animals. The condyle is placed very low — not much higher than the apex 

 of the canine tooth when the bone is resting on a flat surface. It is long trans- 

 versely and the inner part of the articular surface is much the wider and extends 

 over the posterior surface. Its long axis is a little oblique, the inner end being 

 inclined somewhat downward and forward. The coronoid process is very exten- 

 sive and is l:)ent slightly outward and V)ackward. 



The body of the hyoid bone is a slightly curved transverse rod; it is compressed 

 from before backward, and bears no lingual process. The thyroid cornua are 

 permanently attached to the body by cartilage ; they diverge widely, curve inward, 

 and are compressed laterally. The small cornua are short, prismatic, and strong. 

 The middle cornua are commonly a little longcn' than the great cornua; they are 

 compressed laterally, and are slightly enlarged at the ends, which are joined by 

 cartilage to the adjacent cornua. The great cornua are bent outward and are 

 somewhat twisted. 



THE SKULL AS A WHOLE 



The different breeds of dog display great variations in the form and size of 

 the skull. Those which have a long narrow skull {e. q., greyhound, collie) are 

 designated dolichocephalic. Other dogs {e. g., bulldog, small spaniels, pugs) have 

 very broad, short skulls and are termed brachy cephalic. Intermediate forms 

 (e. g., fox terrier, dachshund) are mesaticephalic. 



The length is usually measured from the occipital crest to the anterior end of the premaxil- 



lary suture, and the breadth between the summits of the zygomatic arches. The cephalic index 



is the relation of the breadth to the length, assuming the latter equal 100; the formula is: 



breadth X 100 



, 7^ = cephalic index. The index of extreme dolichocephalic breeds is about 50 or 



length 



even less, as in the greyhound, and that of brachycephalic specimens may be as high as 90, as in 



the bulldog and pugs. Among the mesaticephalic types are the fox terrier, with an index of about 



70, and the white Pomeranian, with one about 72 to 75. The cranio-facial index is the relation 



of the distance from the occipital crest to the fronto-nasal suture to that between the latter and 



the nasal notch. It varies from 10 : 3 in extreme brachycephalic breeds to 10 : 7 in extreme 



dolichocephalic subjects. 



The superior surface shows the wide outward curve of the zygomatic arches, 

 and the great extent of the temporal fossae. The latter are separated by the sagittal 

 crest, which in the larger breeds is very strong and prominent, and is continued by 

 the diverging frontal ridges to the supraorbital processes. The frontal and nasal 

 regions are centrally depressed, and are more or less concave in profile. The nasal 

 region is narrow and is terminated in front by a nasal notch. In the extreme 

 brachycephalic breeds the differences are very striking. The cranium is strongly 

 convex in both directions and is considerably longer than the face. The sagittal 

 crest is more or less effaced and is formed by the interparietal only. The parieto- 

 frontal crests are separated by an interval behind and diverge to the supraorbital 

 processes, so that the temporal fossae are widely separated. The frontal region is 

 wide, strongly convex, and has a shallow central depression. The nasal region is 

 very short, relatively wide, and centrally depressed. In profile there is a marked 



