Is the skull of the Russian sight hound, the Borzoi long, narrow or even both? How about the Chinese Chow-Chow? Is his skull broader than average or does he only seems so because his skull is shorter than others? In order to be able to give an answer to such questions a stable measurement representative for the size had to be found. The skull base length that is still used by many scientists is not suited, as it does not only include the braincase but the very flexible facial and palatal region as well. Such a stable measurement was found and tested here at the Museum: It's the "Hirnstammbasis," the length from the oral edge of the Foramen Magnum (Basion) to the boundary of the Pterygoid and Palatine where it joins the Presphenoid. This measurement helped a great deal in describing numerically and thus objectively size and shape of dog skulls. It could be shown, that the above mentioned Borzoi, often referred to as being dolichocephal (e.g. in Miller's Anatomy of the Dog, p.118, 2nd ed.1979), does not possess a longer skull at all, but in reality is only narrow. The Chow-Chow on the other side, often referred as short-faced and lion-like, shows a significant broader skull than would be expected for his size. There is no reduction of the upper jaw in it's skull.
On the other hand, there are breeds that show a strong shortening of the skull. These are mainly breeds from the molossoid group like the Boxer, the Bullmastiff, the Bulldog, The St. Bernard Dog and -- among many other dwarfs -- the Pug. Their skull shape is referred to as brachycephalic. However these breed do not show a reduction of the whole skull but only of the upper jaw. The braincase stays mainly stable and does not show this tremendous variability. These facts give indication of the relationship between the different parts of the skull (facial - palatal - neural) to each other and of the great plasticity of the structures in the region of the Choanae. A different inheritance of upper and lower jaw is obvious when we take a look at all those breeds that show very different lengths of their upper and lower jaws.
The muzzle may not only be shortened as e.g. in the Boxer, but may experience a more or less accentuated dorsal (upwards) or ventral (downwards) bending. The above mentioned sight hounds and several terriers belong here, as we often see a relative strong downwards bending of the muzzle (Clinorhynchy). As we have mentioned previously, a dorsal bending (Airorhynchy) can be seen as well. This is most common with breeds with shortened muzzles. This accentuates the already short muzzle (e.g. Pug, Pekinese, etc.) even more. Such a phenomena can also be detected with the St. Bernard Dog, as this breed too shows an upward bending of the muzzle.
One other interesting subject is the dependency of brain size from the absolute size of the skull and the occurrence of a Sagittal crest (Crista Sagittalis). Small dogs have a much larger relative brain size than large dogs. This phenomena is known as Haller's law, which says that small individuals from one species have relative larger brains than their larger relatives. The answer to this law lies in the different relations of bodies and surfaces in different sizes. Small dogs have relative larger body surfaces (surface sinks with the root, volume with the third root) and thus more sensory cells in their skin. Furthermore main cerebral centers may not sink below a certain size as to assure their full functionality. This explains the rather "large" heads of small dogs. This has nothing to do with "intelligence"! (One wonders if the dwarf sized breeds are at their minimum at present, or if there's still a lower limit not yet reached).
The mentioned Sagittal crest is a bony protrusion whose growth is induced by the muscles of the jaw. Within certain limits the size of the crest may be modified by strain put upon it from the muscles. But much more important is the absolute size of the skull. A small dog will never be able to grow a Sagittal crest for the simple reason that his skull provides so much area for the muscles of the jaw, that the muscles will never even reach the top of the skull. Only the meeting of the muscles from the two sides of the head an top of the skull will induce the growth of a Sagittal crest. Thus this crest is a means for larger dogs to provide sufficient area for their jaw muscles on their relative small skulls. Such and may other laws are easily verified on our collections.