THE SKULL AS A WHOLE 195 



its length and is a little everted, especiallj^ in its middle; 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 men- 

 tal foramina on either side. The vertical part is relatively small. Its lateral sur- 

 face presents a deep masseteric fossa (Fossa masseterica) which encroaches on the 

 coronoid process and is limited by ridges in front and below. The medial surface 

 is convex and is marked by the usual mandibular foramen. At about the same 

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

 jects 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 fiat surface. It is long trans- 

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

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

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

 sive and is bent slightlj^ outward and backward. 



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 per- 

 manently 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 longer than the great cornua; they are com- 

 pressed 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 dogs display great variations in the form and size of 

 the skull. Those which have a long narrow skull (e. g., greyhound, collie) are 

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

 very broad, short skulls and are termed brachycephalic. Intermediate forms 

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



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

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

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

 breadth X 100 ^ gephahc index. The index of extreme dolichocephalic breeds is about 50, 

 length nr, ■ j-i, J 



as in the greyhound, and that of brachycephahc specimens may be as high as 90, as m the pug and 

 some toy terriers. Among the mesaticephaUc types are the fox terrier, with an index of about 

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

 the distance between the nuchal crest and the fronto-nasal suture to that between the latter and 

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

 dohchocephalic subjects. 



The frontal surface shows the wide outward curve of the zygomatic arches 

 and the great extent of the temporal fossa. The latter are separated by the parietal 

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

 the diverging frontal crests 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 parietal 

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

 parietofrontal crests are separated by an interval behind and diverge to the supra- 

 orbital processes, so that the temporal fossae are widely separated. The fronta 

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

 region is very short,Velatively wide, and centrally depressed. In profile there is a 



