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Table 1 Main developmental events during embryonic development of the naso-palatal complex in the brown anole

From: Development of the squamate naso-palatal complex: detailed 3D analysis of the vomeronasal organ and nasal cavity in the brown anole Anolis sagrei (Squamata: Iguania)

Phase Stagea Facial prominences, superficial palate and choanal groove Nasal cavity VNO Lacrimal duct
Early development 2–3 facial prominences weakly developed nasal pit present; round primitive naris open on the ventrolateral surface of the forming snout vomeronasal pit may appear in some specimen at stage 3 on medial wall of the nasal pit  
5–5/6 paired primordium of the vomerine cushion present; nasolacrimal groove, between the lateral nasal prominence and the maxillary prominence, well visible clearly elongated primitive naris open ventrally; primitive choanal tube and primordia of the: Stammteil, extraconchal space (stage 5/6) and lateral nasal concha (stage 5/6) distinguishable vomeronasal pit well visible on medial wall of the primitive choanal tube
Middle development 6 facial prominences well visible; paired primordia of the vomerine cushion and anterior segment of the palate present anteriormost part of the primitive choanal tube filled with the nasal plug; posterior extension of the nasal pit (part of the primitive choanal tube) well visible vomeronasal pit spherical in shape (early VNO)  
7 frontonasal mass formed; lateral nasal prominence and the frontonasal mass in close apposition through their entire lengths (a); maxillary prominence approaches to the frontonasal mass; maxillary fold present; paired primordium of the anterior segment of the palate almost obliterated early nasal cavity: primordium of vestibulum (still part of the primitive choanal tube) relatively well distinguishable (a); presumptive external naris narrowed (a); the extraconchal space well visible distance between the early VNO and the primitive naris increased  
8 lateral nasal prominence and the maxillary prominence fused with the frontonasal mass (b); paired primordium of the anterior segment of the palate well visible again division of the primitive naris into the external naris and primitive outer choana (b); vestibulum well defined (b); small antorbital space present; extraconchal space well developed, but restricted approximately to the posterior half of the primordial main nasal cavity; choanal diverticulum formed ellipsoidal shape of the early VNO; narrowed connection of the early VNO and the primitive choanal tube primordium of the lacrimal duct present in deep part of the groove between the lower eyelid primordium and the maxillary prominence
9 upper lip and the anterior segment of the palate well formed; vomerine cushion visible as a single structure; choanal fold visible vestibulum of tubular form; vertical orientation of the extraconchal space and its restriction to the posterior third of the main nasal cavity primordium; primitive inner choana, primitive inner choanal tube and the primitive outer choanal tube distinguishable; subconchal fold visible primordium of the VNO duct distinguishable from the anterior most part of the primitive outer choanal tube (early VNO can be considered as the VNO); small primordial mushroom body visible both lacrimal canaliculi visible; anterior part of the lacrimal duct (anterior to the anterior lacrimal canaliculi) independent from the groove between the lower eyelid primordium and the maxillary prominence
9/10–10 anterior part of the primitive outer choana transformed into opening of the choanal groove (c) anterior part of the primitive inner choana closed by fusion of the subconchal fold and the vomerine cushion (formation of the choanal groove) (c); initial bud of the lateral nasal gland well distinguishable VNO separated from the nasal cavity (c) lacrimal duct entirely detached from the groove between the lower eyelid and the maxillary prominence; posterior and anterior lacrimal canaliculi clearly in contact to the inner surface of the lower eyelid
Late development 11–12 anterior third of the choanal groove more widely open to the oral cavity in contrast to the rest part of this structure restricted by the choanal fold and the convex vomerine cushion lateral nasal gland characterized by the main duct primordium and the spherical bud with few clefts; extraconchal space restricted to the posterior end of the main nasal cavity; antorbital space visible as a small vertical diverticulum tubular-like VNO duct; pigment granules present in the central layer of the vomeronasal sensory epithelium (stage 12) rostral plate of the lacrimal duct connected to the anterior half of the choanal groove
14 posterior part of the choanal groove widely open to the oral cavity; opening of the anterior third of the choanal groove narrowed slightly by the vomerine cushion; borders of the anterior segment of the palate obliterated lateral nasal gland composed of many tubulo-acinar units; dorsal part of the extraconchal space drawn out beyond the level of the antorbital space   triangular shape of the lacrimal duct rostral plate (its posterior expansion distinguishable); anteriormost part of the lacrimal duct at the border between the VNO duct and the choanal groove
17 choanal fold well developed; maxillary fold less distinct vestibulum almost horizontal; compound tubuloacinar lateral nasal gland; extraconchal space drawn out posteromedially and dilated (lack the lateral nasal concha, except its anterior extension between the Stammteil and inner choanal tube); sensory olfactory epithelium restricted to the anterodorsal part of the main nasal cavity; entire outer choanal tube dilated cartilage of the mushroom body well distinguishable; two parts of the VNO duct well visible: just ventral to the VNO and anterolateral extension anteriormost part of the lacrimal duct expanded more anteriorly along the medial wall of the VNO duct
18 choanal fold apposed to lateral ridge of the vomerine cushion (opening of the choanal groove to the oral cavity reduced) nasal plug usually reduced or absent; compound tubular lateral nasal gland; lumen of the main nasal cavity increased (dilatated): lateral edge of the extraconchal space almost completely obliterated ventral channel more distinct; rhombus-like shape of the VNO in transverse section; VNO lumen large; vomeronasal sensory epithelium: numerous pigment granules, hyperchromatic nuclei of the cells of basal and central layers posterior expansion of the lacrimal duct rostral plate almost reaching the level of the outer choana; lacrimal duct, including lacrimal canaliculi, usually patent
19 choanal fold fused with vomerine cushion (closed choanal groove formed) nasal plug absent   lacrimal duct, including lacrimal canaliculi, patent
  1. (a, b, c) closely associated developmental events
  2. aaccording to Sanger et al. [54]