. A manual of zoology. Zoology. ir. YERTEBEATA. 521 closed; usually gaps (fontanelks) occur in its roof, and frequently in its floor. Tlie higher the animal intellectually and the larger its brain the more the connective tissue (priiDoriUal cranium) is called ujion to roof in the chondrocranium. Hence it is that in the reptiles, birds, and mammals, where it is also confined to embryonic life, tlie chondrocranium is relatively the smallest. Since it only closes above in the occipital (hinder) region, while it gaps widely in front, it follows that the secondary bones play an impjortant part in t
. A manual of zoology. Zoology. ir. YERTEBEATA. 521 closed; usually gaps (fontanelks) occur in its roof, and frequently in its floor. Tlie higher the animal intellectually and the larger its brain the more the connective tissue (priiDoriUal cranium) is called ujion to roof in the chondrocranium. Hence it is that in the reptiles, birds, and mammals, where it is also confined to embryonic life, tlie chondrocranium is relatively the smallest. Since it only closes above in the occipital (hinder) region, while it gaps widely in front, it follows that the secondary bones play an impjortant part in the completion of the skull. The bony skull presents great difficulties from the standpoint of comparative anatomy, in part from its varying appearance in the different groups, in part on account of the number and com- plicated arrangement of the constituent bones. It may be said in beginning that as a rule the same bone reappears in the se])arate classes, and that the difficulties are connected with the fact that certain bones may fail to develop (Amphibia), or they may fuse to larger elements (mammals). A further complication results from the intimate uuion with the cranium of bones of the visceral arches, which, strictly speaking, do not belong to Fia. '^kuU of carp, the visceral skeleton remnved. (A) CartUage ^â¢es: or6 od, ncs, basl-, ex-, and supraorcipitals ; ../.», ejnotio ; pto P^'' *' ââ ;V'''.";;P' ,f notic- pro prootir ; .-.â .â , alisphenoid ; »s, orbitosplienoid;;»", niesetlmioi 1 ee, ecT- ethmoid. (BWentlal 'brane bones : |..s', parasphenoid ; â¢, vomer. ,C , membrane bones : p, parietal; fr, frontal ; J-4, exits ot nen ts. The primary bones (preformed in cartilage) can l)e divided ac- cordhigto the cranial regions into four groups: (1) bones of the hinder^iart of the }iew\âorcipitaIia; (2) bones of the ear region âotica; (3) bones near the eyeâspheitoiduUa: and (4) of the nasal capsuleâp//*woiV?«./i«. The
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectzoology, bookyear1902
