Reproductive Biology and Embryology of the ... - Seaturtle.org
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402 REPRODUCTIVE SIOLOGY AND EMSRYOLOGY OF CROCODILIANS<br />
STAGES OF EMSRYONIC DEVELOPMENT tAFTER EGG LAYING) 403<br />
Facial Processes. The medial <strong>and</strong> lateral nasal processes are distinct elevations<br />
on ei<strong>the</strong>r side <strong>of</strong> <strong>the</strong> nasal pits. The maxillary processes extend<br />
forward as far as <strong>the</strong> caudal junction <strong>of</strong> <strong>the</strong> medial <strong>and</strong> lateral nasal<br />
processes, <strong>and</strong> delimits a distinct groove beneath <strong>the</strong> eye.<br />
Limbs. The hindlimb bud is fan-shaped with a distinct apical ectodermal<br />
ridge (Fig. 23). It extends out fur<strong>the</strong>r from <strong>the</strong> body wall than <strong>the</strong><br />
forelimb bud.<br />
Tail. The tail is coiled through four 90 0 turns.<br />
Gut <strong>and</strong> Abdominal Organs. The mesonephros <strong>and</strong> liver are clearly visible<br />
through <strong>the</strong> lateral body walls.<br />
Stege 11 [Figs. 1 g end 23]<br />
Facial Processes. The nasal pit slit is starting to form between <strong>the</strong> medial<br />
<strong>and</strong> lateral nasal processes. The club-shaped maxillary processes extend to<br />
<strong>the</strong> junction <strong>of</strong> <strong>the</strong> medial <strong>and</strong> lateral nasal processes <strong>and</strong> is continuous<br />
with <strong>the</strong> lateral nasal process.<br />
Limbs. Both forelimb <strong>and</strong> hindlimb buds extend out caudally from <strong>the</strong><br />
body wall, <strong>and</strong> both have distinct apical ectodermal ridges (Fig. 23). The<br />
forelimb has a distinct constriction demarcating <strong>the</strong> proximal <strong>and</strong> distal<br />
elements, but this constriction is less marked in <strong>the</strong> hindlimb.<br />
Gut <strong>and</strong> Abdominal Organs. A loop <strong>of</strong> midgut tube is visible at <strong>the</strong> level<br />
<strong>of</strong> <strong>the</strong> umbilicus.<br />
Branchial Arches. The 2nd branchial arch continues to overgrow <strong>the</strong><br />
3rd, <strong>and</strong> arches 4 <strong>and</strong> 5 are starting to submerge. The 1st branchial cleft is<br />
immediately ventral to <strong>the</strong> otocyst.<br />
Eye. Distinct black pigment present in <strong>the</strong> iris.<br />
Extra-embryonic Membranes. The chorioallantois extends two-thirds <strong>the</strong><br />
way around <strong>the</strong> breadth <strong>of</strong> <strong>the</strong> shell membrane.<br />
Stage 12 [Figs. 1 g, 23, <strong>and</strong> 27H]<br />
Branchial Arches. The sinusoidal 1st branchial cleft lies above <strong>the</strong> otocyst<br />
<strong>and</strong> its margins show condensations for <strong>the</strong> auricular hillocks (Fig.<br />
27H). The merged conglomerate <strong>of</strong> arches 1 <strong>and</strong> 2 is growing caudally <strong>and</strong><br />
has overgrown arch 3 to reach <strong>the</strong> junction between <strong>the</strong> 3rd <strong>and</strong> 4th arches.<br />
This conglomerate forms <strong>the</strong> base <strong>of</strong> <strong>the</strong> lower jaw, which extends as far<br />
forward as <strong>the</strong> middle <strong>of</strong> <strong>the</strong> lens <strong>of</strong> <strong>the</strong> eye. Arches 4 <strong>and</strong> 5 are small but<br />
visible. The branchial sinus is patent.<br />
Facial Processes. The club-shaped maxillary process extends forward as<br />
a large shelf <strong>of</strong> tissue beneath <strong>the</strong> eye. The nasal pit slits are deepening as<br />
<strong>the</strong> medial <strong>and</strong> lateral nasal processes enlarge. There is a distinct notch <strong>and</strong><br />
furrow in <strong>the</strong> midline <strong>of</strong> <strong>the</strong> face between <strong>the</strong> medial nasal processes <strong>of</strong><br />
each side.<br />
Limbs. The forelimb, which is beginning to bend in <strong>the</strong> region <strong>of</strong> con-<br />
striction for <strong>the</strong> proximal <strong>and</strong> distal elements, lies closer to <strong>the</strong> flank <strong>of</strong> <strong>the</strong><br />
embryo. The elongated hindlimb shows little differentiation into proximal<br />
<strong>and</strong> distal elements, <strong>and</strong> although <strong>the</strong>re is still a distinct apical ectodermal<br />
ridge, foot plate formation is just discernible (Fig. 23).<br />
Stsge 13 [Figs. 1 g, 23, 24A-C, 27H, 34C end 0]<br />
Facial Processes. The nasal pit slits are very distinct (Figs. 24A <strong>and</strong> B).<br />
The prominent maxillary processes are continuous with <strong>the</strong> lateral nasal<br />
processes (Figs. 24A-C).<br />
Limbs. The forelimb is now distinctly bent towards <strong>the</strong> pericardium.<br />
The distal hindlimb is flattened <strong>and</strong> enlarged into a footplate primordium<br />
(Fig. 23).<br />
Branchial Arches. Arch 3 is almost completely overgrown by arch 2,<br />
which now reaches <strong>the</strong> pericardium. Arches 4 <strong>and</strong> 5 are difficult to see. The<br />
branchial sinus has closed. The anterior margin <strong>of</strong> <strong>the</strong> lower jaw has grown<br />
forward from <strong>the</strong> merged conglomerate <strong>of</strong> arches 1 <strong>and</strong> 2. The 1st branchial<br />
cleft is now more horizontally oriented <strong>and</strong> is hereafter referred to as <strong>the</strong><br />
external auditory meatus. The upper ear flap is sinusoidal with a midline<br />
bulge formed by <strong>the</strong> merging <strong>of</strong> <strong>the</strong> auricular hillocks (Fig. 27H). A groove<br />
runs craniocaudally along <strong>the</strong> basal (dorsal) aspects <strong>of</strong> <strong>the</strong> branchial arches<br />
<strong>and</strong> lower jaw.<br />
Extra-embryonic Membranes. The chorioallantois now extends as a ring<br />
around <strong>the</strong> inner circumference <strong>of</strong> <strong>the</strong> central eggshell membrane.<br />
Stege 14 [Figs. 1 g, 23, 240, 27F end H]<br />
Facial Processes. The nasal pit slit has closed due to <strong>the</strong> merging <strong>of</strong> <strong>the</strong><br />
medial nasal, lateral nasal, <strong>and</strong> maxillary processes (Figs. 240 <strong>and</strong> 27F).<br />
The medial nasal processes are prominent <strong>and</strong> have anterodorsal external<br />
bulges (Figs. 240 <strong>and</strong> 27F). These will later grow forward to displace <strong>the</strong><br />
external nares dorsally. The medial nasal processes also have two anterior<br />
intraoral bulges signifying <strong>the</strong> onset <strong>of</strong> primary palate development (Figs.<br />
240 <strong>and</strong> 27F). The maxillary processes have sinusoidal intraoral margins<br />
signifying <strong>the</strong> onset <strong>of</strong> secondary palate development. The internal nares<br />
are distinct.<br />
Limbs. The foot <strong>and</strong> h<strong>and</strong> plates are distinct; <strong>the</strong> former is advanced<br />
over <strong>the</strong> latter (Fig. 23).<br />
Branchial Arches. The 2nd branchial arch has overgrown <strong>the</strong> 3rd, 4th,<br />
<strong>and</strong> 5th, <strong>and</strong> this merged conglomerate toge<strong>the</strong>r with <strong>the</strong> 1st arch forms<br />
<strong>the</strong> base <strong>of</strong> <strong>the</strong> lower jaw <strong>and</strong> <strong>the</strong> neck. A craniocaudal groove is still<br />
present along <strong>the</strong> dorsal margins <strong>of</strong> <strong>the</strong> merged 1st <strong>and</strong> 2nd arches.<br />
Lower Jaw. The lower jaw extends one-fourth <strong>the</strong> way beneath <strong>the</strong><br />
upper jaw. It is broad <strong>and</strong> round in A. mississippiensis but more pointed in<br />
C. johnsoni.