الفهرس 
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Abstract
lIn the present work the development of the skull of the teleost fish
Ctenopharyngodon idella is described in six developmental stages (4, 5,
6, 7. 8, 10. total length) and compared with other bony fishes.
The study was based on graphical reconstruction from stained
transverse sections through the head region of the studied developmental
stages.
The chondrocranium is composed, as in all bony fishes of the
neurocranium and viscerocranium. The study of the development of the
chondrocranium of Ctenopharyngodon idella has shown that the chondral
neurocranium of”tropitrabic type”.
In the morphological description attention has been given to the
shape, position and relative size of the different constituents of the
chondral skull during ontogeny. The relation of the chondral skull with
the brain and main sensory organs are also considered.
1. The neurocranium is originally represented by two trabeculae cranii,
parachordals, and auditory capsules. The auditory capsule arise
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indpendently. The trabecula cranii appears from the beginning in
continuity with the parachordals. All these elements appears in
procartilaginous state in 4mm stage.
2. The trabecula communis is formed by the fusion of the trabeculae
cranii in the S mm larval stage where the neurocranium has
chondrified. In 6mm larval stage, the trabecula communis extends
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anteriorly to form the ethmoid plate. The latter extends laterally to
form the lamina orbitonasalis in 8 mm larval stage.
3. The paired trabeculae cranii enclose the hypophysial fenestra between
them. The trabecula undergoes partially resorption during the
development (10 mm stage).
4. The taeniae marginales are discontinuous during ontogeny. They are
developed early in 7mm larval stage. At the same stage, an incomplete
epiphysial bridge is developed as a finger like process from the taeniae
marginales.
5. The lateral commissure is incomplete, and as development proceeds it
becomes complete.
6. The parachordal plates arise in continuation with the trabecula cranii
they are separated by the notochord in 4 mm larval stage. In 10 rom
larval stage, the parachordals fuse together above the notochord
forming the prootic bridge.
7. The rostral cartilage and the intemasal septum have been noticed in
stages of Ctenopharyngodon idella.
8. The base of the auditory capsule is connected with the parachordal by
a single commissure which is the anterior basicapsular commissure in
the 6 mm larval stage. In 7 mm larval stage, the auditory capsule is
connected with the parachordal by another commissure which is the
posterior basicapsular commissure, lying between the basicapsular ’ .
fenestra and the vagus foramen. In lOmm larval stage, this fenestra is
completely invaded by cartilage, leaving a small foramen for the exit
of the glossopharyngeal nerve.
9. The tectum synoticum develops by the dorsal fusion of the auditory
capsules in 8mm larval stage. It forms the roof of the neurocranium
above brain.
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10. The cranial part of the notochord undergoes a marked reduction in
length during development.
11. The mandibular arch is composed of the palatoquadrate and
Meckel t s cartilage, the two elements appear earlier as independent
structures.
12. Meckel’s cartilage appears at first in a procartilaginous state (S rom)
anteriorly separate from its fellow of the opposite side. At 8 rom
larval stage, the two Meckel t s cartilages become contacted with
each other, the posterior end of each one is differentiated into two
processes; retroarticular processes in 6 rom larval stage and coronoid
process in 7mm larval stage. The palatoquadrate articulates with
Meckel’s cartilage between these two processes by means of the
apophysis.
13. The palatoquadrate articulates with the ethmoid plate by an
ethmopalatine articulation in 7mm stage.
14. The hyoid arch is originally composed of four pieces of cartilage,
three of which are located on each side, i.e, the hyosymplectic,
interhyal and hypoceratohyal in addition to, the median single
basihyal. Such structures are developed as independent structures.
15. There are five branchial arches. The branchial arches J-Ill are
complete, each arch consists of a hypobranchial, ceratobranchial,
epibranchial and infrapharyngobranchial. In the fourth branchial
arch, the hypobranchial are missing. The fifth branchial arch is
represented only by ceratobranchial.
16. The hypobranchials are represented by three cartilaginous structures ..
articuladng with the comapondina ceratobranchials; they develop
independently from other structures of the branchial arches.
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17. The ceratobranchials are the first structures to appear in the
branchial arch. skeleton as independent structures and in
procartilaginous state in the 5 mm larval stage.
18. Two median copulae are developed during ontogeny (anterior &
posterior copulae) on which the hypobranchials (I-Ill) and
ceratobranchials (IV & V), articulate respectively. The anterior
copula is developed in continuation with the ceratobranchial (I) in
the 6 rom larval stage, but the posterior copula is developed as an
independent cartilage in the 7 mm larval’ stage. Posteriorly , the
anterior copula overlaps the anterior end of the posterior copula.
19. The epibranchials are represented by four independent
epibranchials articulating with the corresponding ceratobranchials and
infrapharyngobranchials.
20. The infrapharyngobranchials I-IV make their first appearance in
(lOmm stage). Laterally, the infrapharyngobranchials I-IV articulates
with the corresponding epibranchials. The first infrapharynogbranchial
articulates laterally and posteriorly with the first and the second
epibranchials, respectively. The. second infrapharyngobranchial
articulates at its anterior part with the corresponding epibranchial, and
at its middle and posterior parts articulates with the third epibranchial.
The third infrapharyngobranchial articulate laterally and posteriorly
with the third and fourth epibranchials, respectively.