الفهرس 
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Abstract
In the present work the development of the chondrocranium of the teleost fish Poecilia reticulata is described in seven developmental stages and compared with other bony fishes. The study was based on graphical reconstruction from stained transverse sections through the head region of the studies developmental stages.The chondrocranium is composed, as in all bony fishes, of the
neurocranium and viscerocranium. The former develops earlier than the latter. The study of the development of the chondrocranium of Poedilia reticulata has shown that the chondral neurocranium of “ platybasic type”. The neurocranium is originally represented by two trabeculae cranii, polar cartilage, parachordal,and auditory capsules. The trabeculae cranii arise independently. The auditory capsules appears from the beginning in continuity with the parachordals. Also the polar cartilage chondrify with the parachordals and thus give rise to the “ parachordopolar bars”. All these elements appears in procartilaginous state. The two trabeculae cranii at first represented by two short rods which are widely separated from each other. However in stage III the anterior end of trabecula cranii fused together forming trabeculae communis. This latter structure extends anteriorly to form the ethmoid plate. The plate does not extends forward as a rostrum. The lamin-aeorbitonasalis extends .