الفهرس 
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Abstract
!he study ot the development ot the skull 1s boand up
with the recognition ot the two materials, cartilage and
bone ,of which the skull 1s mainly composed, and with the
theories concerning the relations of these tissues to ODe
another, both anatomically and developmentally.
According to De Beer (1937) the earliest attempt tor
the distinction between cartilage and bone as 8kelet~ materials
appears to be that of Aristotle who contrasted the
~hondr1chthyes with the Osteichthyes. However, it was a
long time before closer study of developmental stages revealed
that the fact that some bones were preceded by cartilaginous
structures of similar shape which they replaoed,
while other bones arose directly from connective tissue
membranes without cartilaginous precursors. !he former are
customarily ref.~red to as cartilage bones, and the latter
as membrane bones.
The cartilaginous skull, or chondrocranium, B8 a whole
was recognized for the first time by Arendt (1822), then
Von Ba.er (1826) put forward the view of ”inner” and ”ollter”
skeletont based on his studies of fishes. The ”inner skeleton”
was composed of the chondrocranium together with its
embedded bones and co~ering bones, and was contrasted with
the II outer skeleton” represented by the bony dermal scales.
· ’_c’l’~--;+r---<--’O--.--------~.-_._--.-~--’-”_._’-_ ..’r- ~_”_~r_ .-
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The existence ot a chondrocranium in earlJ stages of
all vertebrates was recognized by Reichert (1838), who followed
the aevelopment of the visceral arch skeletoD, and
further distinguished between cartilage bones (or replacina
bones), and membrane bones. The next advance was made
b.r AgassiZ (lB44) who classified the bones o~ fish skulls
into ossifications of the chondrocranium and protective
plates, which latter include not only the superficial dermal
ossifications but also the more deeply seated bones surrounding
the chondrocranium, and therefore represent the entire
category of membrane bones.
A synthetic description of the mechanical units forming
the skull has been made b,y Verraes (1973), who classified the
skeletal elements in the 97 rom juvenile stage ot the teleost
fish Salmo Sairdperi into seven units; viz., the neurocranium
( including sensory capsules), the suspensoriwm ( • the cartilaginous
upper jaw + hyos,ymplectic and their associated
bones + preopercular bone), the operculum ( the operele ,
. subopercle and interopercle bones), the secondary upper jaw
(premaxilla, maxilla), the lower jaw ( Meckel’s cartilage
and its associated bones + secondary lower jaw bones), the
hyoid ( ventral elements of the hyoid arch) and the branchial
arches.
The development of the skull of a number of species
representing different families of bony fishes has been a
subject of various investigators. Thus, Norman (1926) stUdied
~---...,.....- -~.- - _ .....,...,..., _._- .------’”---- _.__ .,
OIIarkhab (1950) .tud1ed the de.•elopmeDt .~ the ohoadrocraa1wa
of JrotoptllQ,’ chi tala ( fam117 Notopter1dae) 1D
co.parison with that ot Salmo and of GY!ID!lCh98. The stud7
Showedthat Notapterae has no close resemblance to GYmA~~
but is more like the generalized clupieform chondroeraniwa
of SalJll(h The same author stated that, in the cha-
Ddrocranium of Notoptertts , the myodomes are abseat, iDd
there 1s no interorbital septum.
SrloivasBchar (1953), described the chondrocranium of
eight stages of Ophicepha1us gachua commencing from the first
day to the twenty fifth dq after hatching. He stated that,
the trabecllla. and parachordal arise independent1.1’. !he rostral
cartilage is developed independently, it is not fused
with any part ot the ethmoid plate. The same author fOWld
that the basicapaular fenestra and the metotic foramen are
•• parated b7 the basl .•e.t1bular commissure, there i8 DO tectum
posteriLls. The qu.adrate i8 la.sed with the h7011laDdibalar
aDd the pterygoid process ot the palatoquadrate 1s di8coat1n-
110U8 with the qLladrate.
Abdel Az1z(1957)stud1ed the development of the chondrocranium
of Tilapia zil11 ( family Cichlidae). She found
that, the nellrocranium is typically ” tropiba81c· aDd 1s
deYeloped earlier during olltogelJ7”than the splanchDocranium.
The same author stated that the trabeculae,polar oartilage.
aDd parachordals arise as independent structures while the
au.d1tory capsules appear 1n continuity with the parachordal ••
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8zteDdlq trom the aud1 t017 capsule up to the e’thmo1d repoD
oD each s1de ot the neurocraa1um. Ue also established that,
the lDtraph&17Dgobruchials .of the f1rst tour branchial
arches are tused together to torm a single cartilaginous
pl~e.
Pashlne & .arethe (1977) studied the chondrocranium
ot some stages ot Clprious carpio (family Cyprinidae). They
showed that, the chondrocranium is of the” tropltrab1c ”
type, and the parachordals are connected to the sud1 tory
capsules by means of bas1capsular and baslTestibular commis,
sares. The same authors added that the basih7al and the
basibranchials form a common copula which breaks up into two
copulae.
Ismail (1919) studied, from a functional view point,
the postembryonic development of the skull of the c!chl1d
fish Haplochrom1. elegans which represents a generalized
insect! Torous Haplochrom1s from the east - African lakes,
Edward and George, 1n comparison with other teleost tishe.,
especially ~ gairdneri ( family Salmonldae; Varraes,
(1974 b)”. The study revealed that the neLlrocranial
floor is of the” tropitrabic” type aDd that the neurocranial
pharyngobranchiad apophysis, which is characteristic
of the cichlld neurocranlwn, is developed as a Tentral projection
of the neurocranial base in the otic region. The
fourth hypobranchials are absent. An interorbital septum
is present. The taenia tecti medialis posterior originates
-----~~--~------
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aDato~ ot head con8ti1~ent8 in 80me bo~ fishes (Isma11,
1979; Verrae. &: Ismail, 1980; H~sgeane et a1., 1981 ;
Ismail Be: ElshBbka. 1982 ·and Ismall, 1984)·.
In the present work, the development ot the chondrocranium
ot Gamba.ia atlin!s &ffinis is studied in detail.
Attention is given to the change in shape, position, and
relative size of the chondral parts during ontogeJ’JY’ and to
the relation between the developing chondral parts and
~ephalio sensor,yorgans such as the brain, eyes, oltactor,r
organs and.membranous labyrinth. The osteooranium, ho.eYer,
i8 partially described among the chondrocranium especiBl1.7
those bones of the 19 IDOl larval stage. Comparison with
other fishes is also made. The morphological description
of the stUdied parts of the skull during ontoge~ i8 mainly
based on graphical reconstructions as well as OD serial
sections of the studied specimens.
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Larger specimens .ere decalcified by using ED! A
solution (Ismail, 1979) for a period of 10 - 60 dars depending’on
the size of the specimen. The decalcifying solution
was renewed eTery four d91’s. Early developmental
stages. howeTer. were treated as such without decalcification.
Decalcified specimens were~ro~ghly washed under tap
water for 5 - 24 hours depending on the size of the speciman
aDd finallY with distilled water, to remove all traces o~
the decalcifying solution. The specimens were refixed in
Bouln’s fluid.
Dehydration was done by using up-grading series ot etbyl
a1cMol.
Clearing was made in qloL il:owever. terp1neol._
used in some small specimens and showed best result ••
CJ.eard specimens were embedded in melting paraplast VB1”*-
drih wax.
It was found that, in the large specimens, the buccopharyDgeal
canty contains a lot of air-bubbles eTeD a:tter
complete embedding, so that ••beddl:qot· SLl ••. ·~ was
carried out under vacuum.
In order to obtain the best possible histological series
of sections from which graphical reconstruction of different
planes can be made a special procedure tor orientatloD,
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embedding aDd c~ttlng was empl07ed following a t.chniq~.
described b7 Verraes (19748).
~ small liver stripe ot Rabbit with two previously cut
flat sides was oriented and embedded in the same paraffin
block underneath the original specimen, s~ch a stripe is
important as reference mark for the purpose ot making graphical
reconstructions in lateral or medial view.
Serial transverse sections (8 - l~~ thickness) 6f the
head region ot about 16 specimens, comprising seven developmental
stages were prepared.
Serial paraffin sections were stretched separatel1 b.1
passing them through two petrl-dishes containing 5~ solution
ot ethyl-alcohol and warm 0.25 ~ gelatin solution at a temperatu.
re of about 10 degre. below the meltlngpointcf’the . paraffin
used in embedding. Stretched paraffin sections were
permanently mounted and arranged on marked glass slidese The
o
sections were dried overnight at 37 c.
The prepared sections were stained with Delafield’ 8
haematoxylin Rnd eosin, Mallory’s triple stain and
Heidenha1n’a azan stain.
Alizarin-stained whole mount transparencies preparations
were also made which proved best for demonstrating bone fo~-
ation especially ror older stages.
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c. Draw1ng,s:
A good series of transverse sections of each ot the
studied stages was chosen and drawn ’.y ~ehelp of’ • projector.
Prom these drawings projections ot the studied head parts
( oar1i11ace,bone. _d .head OO!ltour) ,. notochord. olfacto17
organa and brain were made in horizontal and vertical longitudinal
planes on millimeter papers. To STaid cODf~.ioD
eyer” structure was projected on a se~arate paper. b7 measuring
its extensions with a compass to the axis ot bilateral
symmetry’ and to the reterence line ot the liver stripe
respectivelY. from the transverse serial sections~&raphical
reconstructions ill’ dorsal • ventral and .;:lateral ne••
were made. By uslI1g this graphical reconstruction technique
It was ea~ to make comparisons between ditferent structures
dtiring ontogeny.
Photomicrographs of some sections were also made to
ill~strate the text.
The following marks are used in the graphical reconstructions
and drawings :
broken lines or poillts represent procartilaginous el&~~9J
- finely or heavily stippled areas represent cartilaginous
elements;
thick or heav,y lines represent bo~ elements.
·34 t;&?-l48 , $
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8- Lateral line incomplete on head and disrupted on body.
2h1raoj,ril’tiC. of the f’am1~ CYpr1nodgntlda. W
h~~&t’~Bt!
Th1. family 18 a y.ry large family and i. repr••• nted
in tropical,warm and ’b;;tmperatcelimates.The family is rich in
dwarf’ species which are more or les8 carp-lilee, but di~
from the true carps (which are charRcterized by a toothless
mouth) by the complete bordering of bones of the jaws and
phary’nx with comb-like teeth, so that they are usua.lly called
toothed carps.
Tbe family exihlb1ts the f9110wing peculiarities:
1. The upper surface of the head is usually flattened.
2. The moll th is terminal and diree ted slightly upward S t the
upper margin of the mouth is bounded only by the pre._-
illaries, which are very freely movable and therefore
render the mouth eminently.
J. N9 barbels.
4. Dorsal fin usually inserted well forward. No adipose fin.
Caudal fin rounded or flag-like, usual~ depending on
whether female or male. Anal fin in the male of 11va-bearing
species 1s wholly or partly modified as an intromittent
or copulator.1 organ (Gonopodium).
5. Scales cycloid and almost always large.
Gambusla !~f1Qis affinjs is o~of the live - bearing
toothed carps; it is usually kOOwQ as mosquito fish or spotted
Qtmbus1a (Sterba & Habl1, 1973).