. Bensley's Practical anatomy of the rabbit : an elementary laboratory text-book in mammalian anatomy. Rabbits -- Anatomy. THE SKULL 53. Fig. 29. Transverse section of shark vertebra Ccartilage stage), from young specimen of Atlantic dogfish, Acanthias: i, intercalary cartilage, com- pleting arch; n, notochord; V, body of vertebra. The Skull Composition of the Skull The head skeleton of a mammal, usually but inaptly called the skull, is a complex of individual bones and cartilage, the arrangement and functions of which may be determined with a Httle effort. The general disposition of the bone
. Bensley's Practical anatomy of the rabbit : an elementary laboratory text-book in mammalian anatomy. Rabbits -- Anatomy. THE SKULL 53. Fig. 29. Transverse section of shark vertebra Ccartilage stage), from young specimen of Atlantic dogfish, Acanthias: i, intercalary cartilage, com- pleting arch; n, notochord; V, body of vertebra. The Skull Composition of the Skull The head skeleton of a mammal, usually but inaptly called the skull, is a complex of individual bones and cartilage, the arrangement and functions of which may be determined with a Httle effort. The general disposition of the bone elements, demonstrable in the rabbit or any mam- mal is as indicated in Fig. 30. Briefly, there is a linear series of basal segments, comprising from behind forward basioccip- ital, basisphenoid, presphenoid, and mes- ethmoid. The three first-named form the floor of the brain-case, while the meseth- moid forms the nasal septum. Associated with the basioccipital are paired, lateral exoccipital bones, and a supraoccipital element, together forming an occipital ring enclosing the aperture for trans- mission of the spinal cord from the cranial cavity (Fig. 25). In ancestral tetrapods, the basioccipital and exoccipital bones took part in the formation of a single rounded condyle for articulation with the first vertebra. In mammals, however, the posterior end of the basioccipital has become reduced, leaving only the two lateral components of the original condyle to make this articulation. Hence the mammal has paired occipital condyles, borne upon the exoccipital bones only and constituting a stronger joint with motion practically restricted to the vertical plane. The basisphenoid and presphenoid bear lateral expansions, respectively the greater and lesser wings, or alisphenoids and orbitosphenoids, which assist in the formation of the side walls of the brain-case. The bony capsule (periotic bone) lodging the internal ear on either side is solidly built into the lateral cranial wall b
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