. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fig. 50.—Biagkammatic Transverse Sections oe the Head in Embryo— (A) Sturgeons, Elasmobranchs, Anukans, and Mammals ; (B) Urodeles AND Snakes ; (C) Certain Teleosteaks, Lizards, Crocodiles, Chblonians, and Birds. Tr, trabeculse cranii; (?, brain ; A, eyes ; Ps, parasphenoid ; IS, interobital septum ; F, frontal; Olf, olfactory nerve. We must now further follow the processes of growth, start- ing from the primary. FI' EiG. 51.—Later Stage in the Development or the Prim- ordial Skull. C, notochord ; B, basilar plate; Tr,
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative. Fig. 50.—Biagkammatic Transverse Sections oe the Head in Embryo— (A) Sturgeons, Elasmobranchs, Anukans, and Mammals ; (B) Urodeles AND Snakes ; (C) Certain Teleosteaks, Lizards, Crocodiles, Chblonians, and Birds. Tr, trabeculse cranii; (?, brain ; A, eyes ; Ps, parasphenoid ; IS, interobital septum ; F, frontal; Olf, olfactory nerve. We must now further follow the processes of growth, start- ing from the primary. FI' EiG. 51.—Later Stage in the Development or the Prim- ordial Skull. C, notochord ; B, basilar plate; Tr, trabecula, which has united with its fellow in front of the pituitary space to formtheethmo-nasal sep- tum {S); Gt, cornu trabe- culae, and AF, antorbital process, which support the olfactory organ (NK) in front and beliind ; 01, for- amina for exit of the olfac- tory nerves from the crani- um ; PF, postorbital pro- cess of trabecula ; A, eye ; O,- auditory organ. condition described above, in which the trabeculae have united together in the middle line. The cartilaginous basal plate now comes into relations with the olfactory, optic, and auditory organs (Fig. 51), around which carti- laginous capsules are formed. Thus an olfactory, an orbital, and an auditory region are early differentiated. The olfactoi-y and auditory capsules, especially in higher types, then become more and more drawn in to the skull proper, and the lateral edges of the basal plate begin to grow upwards round the brain on both sides, eventu- ally extending even to the dorsal region. Thus a continuous cartilaginous capsule is formed, such as persists throughout life in Elasmobranchs for example. But in by far the greater number of Vertebrates, the cartilage does not play so great a part, and is, as a rule, con- fined to the base and lower parts of the sides of the skull and to the sense- capsules, except in the occipital region, where it always extends over the brain. The rest of the skull, more parti
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
