. The biology of the frog . enabled to glide overeach other with little friction. Organs outside of the Body Cavity. — Above the ccelomthere is a second cavity surrounded by the bones of the ver-tebral column and skull and containing the central nervous 8o THE BIOLOGY OF THE FROG system. This neural cavity, as we may well call it, extendsfarther forward than the coelom, and is separated from thelatter by the bases or centra of the vertebrae. The anterior portion of the central nerv-ous system, or brain, liesin the skull, and is contin-br ued posteriorly as the spi-nal cord, which is inclosedwi
. The biology of the frog . enabled to glide overeach other with little friction. Organs outside of the Body Cavity. — Above the ccelomthere is a second cavity surrounded by the bones of the ver-tebral column and skull and containing the central nervous 8o THE BIOLOGY OF THE FROG system. This neural cavity, as we may well call it, extendsfarther forward than the coelom, and is separated from thelatter by the bases or centra of the vertebrae. The anterior portion of the central nerv-ous system, or brain, liesin the skull, and is contin-br ued posteriorly as the spi-nal cord, which is inclosedwithin the vertebral col-umn. If we make a crosssection through the frogsomewhere near the middle,we shall find that the bodycontains two longitudinalcavities separated by thecentra of the vertebrae,—the ccelom below, and theneural tube above. Aroundboth of these is a layerof muscles which is muchthicker dorsally although itcompletely surrounds theccelom below. And outsideof the muscles, from whichit is separated by large. FIG. 13. — Organs in the neural anterior part of tins cavity con-tains the brain, which is composed ofthe olfactory lobes, olf. I; the cere-bral hemispheres, crb. h; the di-encephalon, diet?; the optic lobes,opt. I; cerebellum, cblm; and me-dulla oblongata, med. obi. n. c, neu-ral canal; sp. cd, spinal cord endingin the filum terminale, f. t; e, eye.(After Parker and Parker.) lymph spaces crossed by a few bands of connective tissue,is the skin. With the exception of the loose attachment of the skin,all the features of structure mentioned in the last paragraphbelong to the vertebrate animals in general. We have nextto see how these fundamental features of structure came tobe established. THE DEVELOPMENT OF THE FROG CHAPTER VTHE DEVELOPMENT OF THE FROG The frog, like all higher animals which are developedthrough sexual reproduction, begins its existence as a singlecell, the ovum or egg. The eggs or ova arise in the ovary,and, when full grown, bre
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