CONFORMATION AND EXTERNAL FEATURES

Conformation varies much more considerably in dogs than in other domesticated species. The preferences of fanciers have produced a variety of breeds that are strik­ingly different from each other and from their common wolf ancestor.

The appearance of the dog’s head is largely deter­mined by the shape of the skull, the position and size of the eyes, and the form and carriage of the ears. The ears may be held erect, hang from the side, or have an intermediate carriage that is erect at the base and pen­dulous toward the tip. Certain differences are perma­nent attributes of a breed, but others are no more than temporary expressions of mood.

The skull of the adult dog is characterized by a well- developed facial part, large orbits and temporal fossae, incomplete postorbital bars, prominent tympanic bullae, and the absence of supraorbital foramina. It is widest behind the eyes, where the zygomatic arches are widely spread. Breed differences in the skull largely relate to the relative length of the facial part. Dolichocephalic, brachycephalic, and mesaticephalic or mesocephalic (long, short, and intermediate head length, respectively) breeds are recognized (Figure 11-1). In dolichocephalic breeds like the Greyhound, the head is long and narrow. The dorsal surfaces of nose and cranium form two nearly parallel planes that are divided at the level of the eyes by a break (nasofrontal angle or stop) where the cranium descends to the level of the nose. The long facial part is often accompanied by an underbite jaw (brachygnathism). The external sagittal crest is well developed for attachment of the temporal muscles, and the zygomatic arches project less than in the other

Figure 11-1 Representatives of dolichocephalic (A), mesaticephalic (B), and brachycephalic (C) breeds.

groups. In brachycephalic breeds, like the English Bulldog and the Pekingese, the facial part is short and the cranium wide and globular. The stop is pronounced, and the dorsal surface of the cranium is convex and has a much reduced external sagittal crest. In some breeds the fontanelles remain open throughout life. Numerous skin folds mark the face, and the eyes are widely spaced. Brachycephalic breeds are most often prognathic; the term indicating that the lower jaw protrudes in front of the upper jaw (Figure 11-1, C). Most breeds belong to

Figure 11-2 Clear sign of aggressive intent of a dog.

Figure 11-3 Graying beginning at the upper lip and around the eye.

the mesaticephalic type, in which the length of the skull is more harmoniously proportional to its width.

The face of the dog is more expressive of emotion than that of other species, and everyone is familiar with the signs that indicate aggressive intent (Figure 11-2), submission, or pain, even if unable to particularize them. Age is also clearly revealed in dogs of pigmented coat by a “graying” that begins at the upper lip and later spreads, reaching the area about the eyes by about the eighth year or a little later (Figure 11-3).

Redundancy of facial skin is a feature of several breeds such as the Bulldog, Shar Pei (Figure 11-4), and Bloodhound. In extreme form it may result in frontal folds that obscure the vision, and because the upper eyelid is turned inward (entropion), it may irritate the cornea through contact with hairy skin.

Figure 11—4 Redundancy of skin in a Shar Pei.

In cats, in contrast to the breeds of dogs recently mentioned, the bare sufficiency of the skin of the scalp creates problems when it is necessary to close large wounds.