http://en.wikipedia.org/wiki/Sagittal_crestA sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others.
The presence of this ridge of bone indicates that there are exceptionally strong jaw muscles. The sagittal crest serves primarily for attachment of the temporalis muscle, which is one of the main chewing muscles. Development of the sagittal crest is thought to be connected to the development of this muscle. A sagittal crest usually develops during the childhood of an animal in conjunction with the growth of the temporalis muscle, as a result of convergence and gradual heightening of the temporal lines.
A sagittal crest tends to be present on the skulls of adult animals that rely on powerful biting and clenching of their teeth, usually as a part of their hunting strategy. Skulls of some dinosaur species, including tyrannosaurs, possessed well developed sagittal crests. Among mammals, dogs, cats, lions, and many other carnivores have sagittal crests, as do some leaf eaters, including tapirs and some apes.
http://www.nmbe.ch/research/vertebrates ... s-examplesThe 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.