Talk:2010 Lab 6

From Embryology


From BGD

adenohypophysis - (anterior pituitary, pars distalis) The anterior part of the pituitary, which develops in the early embryo from a transient region on the roof of the pharynx called Rathke's pouch.

adontia - Term used to describe the total lack of tooth development.

allantois - An extraembryonic membrane, endoderm in origin extension from the early hindgut, then cloaca into the connecting stalk of placental animals, connected to the superior end of developing bladder. In reptiles and birds, acts as a reservoir for wastes and mediates gas exchange. In mammals is associated/incorporated with connecting stalk/placental cord fetal-maternal interface.

amnion - An [E.htm#extraembryonic_membrane extraembryonic membrane] ectoderm and extraembryonic mesoderm in origin and forms the innermost fetal membrane, produces amniotic fluid. This fluid-filled sac initially lies above the trilaminar embryonic disc and with embryoic disc folding this sac is drawn ventrally to enclose (cover) the entire embryo, then fetus. The presence of this membane led to the description of reptiles, bird, and mammals as amniotes.

amniotic fluid - The fluid that fills amniotic cavity totally encloses and cushions the embryo. Amniotic fluid enters both the gastrointestinal and respiratory tract following rupture of the buccopharyngeal membrane. The late fetus swallows amniotic fluid.

anacephaly - Neral developmental abnormality, incomplete development of cerebral hemispheres and cranium. Usually related to neural tube defect at the anterior (cranial) neuropore.

anlage - (German, anlage = primordium) Term used to describe a developmental structure, tissue or cells which will form a future structure.

anosmia - Abnormality of having no sense of smell.

anterior neuropore - (rostral, cephalic, or cranial neuropore) The initial "head end" or brain end opening of the neural tube before it closes (humans approximately 24 days postfertilization). The opening at the other "tail end" of the neural tube is the [P.htm#posterior_neuropore posterior neuropore]. The anatomical location of the anterior neuropore in later brain development is the lamina terminalis, lying behind the pituitary gland. Failure of anterior neuropore to close leads to the neural tube defect (NTD) [#anacephaly anacephaly]. (More? Neural Abnormalities | Neural Tube Defects)

aquaeductus vestibuli - (Latin, aquaeductus vestibuli) See [V.htm#vestibular_aqueduct vestibular aqueduct], a tubular component of the inner ear.

arachnoid - (Greek, arachne = spider + -oeides = form) A meshwork (spider web-like) connective tissue covering of the central nervous system, forms part of the meningial layers. Lies between tough outer duramater and fine piamater.

Arnold-Chiari Malformation - A type of malformation which appears multifactorial (including inherited and acquired). Cerebellar tonsils elongate and herniate through foramen magnum into spinal canal, resulting in compression of parts of the brain and spinal cord, and disruption of cerebrospinal fluid flow. Thought to be fundamentally the same as anencephaly and spina bifida.

auricular hillocks - External ear (auricle) embryonic origin, a series of 6 external "bumps" three on each of pharyngeal arch 1 and 2.

Automated Auditory Brainstem Response - (AABR) The basis of a neonatal hearing test that uses a stimulus delivered through earphones and detected by scalp electrodes. Computer ananalysed electrical measurement of activity through nuclei in the hearing central neural pathway.

axial mesoderm - Alternative name for the [N.htm#notochord notochord], an early embryonic structure lying in the midline of mesoderm within the early trilaminar embryo.

axial process - The precursor to the notochord. In the early embryo (week 3) epiblast structure extending from the primitive node (Hensens node) crainally, which will eventuall differentiate to for the [N.htm#notochord notochord], the mesoderm structure that later replaces the axial process. (More? [N.htm#notochord notochord] | Neural Notes | Week 3 Notes)

Barker Hypothesis - ([F.htm#Fetal_Origins_Hypothesis Fetal Origins Hypothesis]) Term named after the researcher, Barker who began a statistical analysis in the UK, of low birth weight data (early 1900's). The hypothesis has since been renamed as the Fetal Origins Hypothesis and proposes that in utero influences can lead too permanent changes in embryo/fetus, low birth weight, which predisposes to chronic disease in adult life.

brain - The general term for the central nervous system (CNS) component formed initially from the cranial end of the neural tube. The remainder of the CNS is the spinal cord. The brain forms initially as 3 primary brain vesicles which later form 5 secondary brain vesicles. (

branchial arch (pharyngeal arch) (Greek, branchia = gill) is a misnomer.

buccal - (Latin, bucca = cheek) A term used to relate to the mouth (oral cavity)

buccopharyngeal membrane - (oral membrane) (Latin, bucca = cheek) A membrane which forms the external upper membrane limit (cranial end) of the early gastrointestinal tract (GIT). This membrane develops during gastrulation by ectoderm and endoderm without a middle (intervening) layer of mesoderm. The membrane lies at the floor of the ventral depression (stomadeum) where the oral cavity will open and will breakdown to form the initial "oral opening" of the gastrointestinal tract. The equivilent membrane at the lower end of the gastrointestinal tract is the [C.htm#cloacal_membrane cloacal membrane].

calvaria - The skull formed from frontal, parietal and occipital bones.

Carnegie stages - Carnegie stages are a system of classifying embryonic development based on the external features and related internal changes that affect appearance and growth of the embryo. Note that the stages are not directly dependent on either age or size, but upon the appearance of specific embryonic features. Early human and other species embryos can be classified by these stages. The term "carnegie stages" are named after the famous USA Institute which began collecting and classifying embryos in the early 1900's.

cartilage - The connective tissue formed from mesoderm by the process of chondrogenesis. In the embryo cartilage initially forms most of the skeleton and is later replaced by bone (ossification). In the adult, cartilage is found in many skeletal regions including the surface of bone joints.

central canal - The lumen or cavity of neural tube lying within the spinal cord. This space is continuous with ventricular system of the brain.

cephalic - (Greek, kephale = head) Term used to relate to the head or sometimes towards the upper body.

cerebellum - (Latin, cerebellum = little brain) A central nervous system component formed from the rhombencephalon (hindbrain) region of the neural tube. The cerebellum is required for coordinated motor activities. Cells within the cerebellum are formed by the ventricular zone of the roof of the fourth ventricle and the second germinal zone (Rhombic lip).

cerumen - The ear wax which is secreted by apocrine glands in the ear canal (external auditory meatus).

cervical flexure - The most caudal brain flexure (of 3) between spinal cord and rhompencephalon.

cervical sinus - An ectodermal depression visible externally during embryonic development (approx carnegie stage 14-16), which marks the region where 2nd pharyngeal arch has grown over 3rd and 4th arches.

chondrocranium in humans, forms base of skull (in lower vertebrates encases brain).

chondrogenesis - the process of forming cartilage, which is a connective tissue formed from from mesoderm (or neural crest in the head region). In the embryo, cartilage initially forms most of the skeleton and is later replaced by bone (ossification). In the adult, cartilage is found in many skeletal regions including the surface of bone joints.

cleft - An anatomical gap or space occuring in abnormal development in or between structures. Most commonly associated with cleft lip and cleft palate. Term is also used to describe the groove that forms between each pharyngeal arch during their formation.

cleft lip - An abnormality of face development leading to an opening in the upper lip. Clefting of the lip and or palate occurs with 300+ different abnormalities. Depending on many factors, this cleft may extend further into the oral cavity leading to a cleft palate. In most cases clefting of the lip and palate can be repaired by surgery.

cleft palate - An abnormality of face development leading to an opening in the [P.htm#palate palate], the roof of the oral cavity between the mouth and the nose. Clefting of the lip and or palate occurs with 300+ different abnormalities. In most cases clefting of the lip and palate can be repaired by surgery.

coelom - Term used to describe a space. There are extraembryonic and intraembryonic coeloms that form during vertebrate development. The single intraembryonic coelom will form the 3 major body cavities: pleural, pericardial and peritoneal.

congenital - Already present at birth, often used to describe defects present at birth, congenital defects.

cranial flexure - (= midbrain flexure) The most cranial brain flexure, between mesencephalon and prosencephalon, of the three flexures (bends) that develop as the nueral tube grows and elongates.

craniofrontonasal syndrome - (CFNS) A human X-linked developmental disorder caused by a mutation in ephrin-B1 affecting mainly females. Characterised by abnormal development of cranial and nasal bones, craniosynostosis (premature coronal suture fusion), and other extracranial anomalies (limb polydactyly and syndactyly).

craniopharyngioma - A common destructive tumorogenic lesions of the hypothalamus and pituitary gland. Can occur when remnant cells from Rathke's pouch remain forming a tumour.

craniosynostosis - The term describing the premature closure of the skull sutures, or fusion of skull bones. May cause skull and brain abnormalities. There are at least 8 different disorders with six related to the fibroblast growth factor receptor (FGFR); Pfeiffer syndrome, Apert syndrome, Crouzon syndrome, Beare-Stevenson syndrome, FGFR2-related isolated coronal synostosis, Jackson-Weiss syndrome, Crouzon syndrome with acanthosis nigricans (AN), and Muenke syndrome.

critical period - (critical period of development) The term used to describe a developmental time when exposure to a teratogen can lead to a developmental abnormality, which can be further divided into an early major and later minor developmental abnormality. The defined critical period will differ in timing and length for different systems.

CRL - Acronym for Crown-Rump Length. Used in embryology to accurately stage the early embryo. Used in clinical ultrasound as a measurement between the periods of 7 to 13 weeks as an accurate estimation of the gestational age.

Crown-rump length - (CRL) A measurement used in embryology to more accurately stage the early embryo. Measured from the curvature at the top (crown) to the curvature at the bottom (rump) of the "C-shaped" early embryo. Used in clinical ultrasound as a measurement between the periods of 7 to 13 weeks as an accurate estimation of the gestational age.

dentin - The bone-like material in body of tooth, lacks osteocytes.

dentin phosphophoryn - (DPP) is part of dentin sialophosphoprotein (DSPP) synthesized in both mesenchyme and epithelium, involved in two developmental processes: epithelial-mesenchymal interactions and branching morphogenesis.

ectoderm - (Greek, ecto = outside + derma = skin) One of the initial 3 germ cell layers, which will form the nervous system from the neural tube and neural crest and also generates the entire epithelial layer of the skin covering the embryo.

ectomesenchyme - The term used to describe ectoderm derived neural crest which contributes in the head region skeletogenic mesenchyme (cartilage, bone, and connective tissue) which in the body region are typically derived from mesoderm.

embryonic period - (embryonic stage, organogenic period) In humans, the first 8 weeks of development is considered the embryonic stage and is divided into 23 Carnegie stages based upon developmental milestones. This has also been described as the "organogenic period". The following time (week 9 to 36) is considered the fetal period.

eminence - An anatomical description for a narrow extension from a larger structure. Synonyms: tuberosity, a protuberance.

endochondral ossification - (Greek, endon = within) The term used to describe the process of replacement of cartilage, which forms the first embryonic body skeleton, with bone. The osteoblasts are the bone-forming cells.

endocrine - (Greek, endon = within) Glands which release hormones into the blood stream. There are many specialized organs and tissues that release hormones into the bloodstream.

endocrine gland - (Greek, endon = within) A gland (organ, tissue) that is specialized for secretion of a hormone into the bloodstream for general circulation.

endoderm - (Greek, endo = inside + derma = skin) One of the initial 3 germ cell layers, formed by the process of gastrulation. The endoderm forms as a cuboidal epithelium and contributes not only to the trilaminar embryo, but also lines the yolk sac. It will form the entire epithelial lining of the gastrointestinal tract (GIT), contribute to the accessory organs of GIT and also forms the epithelial lining of the respiratory tract. Note that in the GIT it contributes both epithelium and the associated epithelial glands. In humans, endoderm forms during week 3 of development.

endolymphatic sac - (Greek, endo = inside) An inner ear structure of the membranous labyringth that has anatomically both an intraosseous and extraosseous component. The sac is connected to membranous labyringth by the endolymphatic duct and has functions regulating endolymph that are both secretory and absorptive. Also the site of endolymphatic sac tumours (papillary cystadenoma of the vestibular aqueduct) either occurring sporadically or associated with the autosomal-dominant von Hippel-Lindau (VHL) disease, due to a germ line mutation.

epiglottis - (Greek, epi = above, upon; glotta = "tongue") cartilaginous part of the larynx above the glottis, which in infancy directs food into the esophagus and not the trachea. Embryologically it develops in the foregut from the hypobranchial eminence, behind the undeveloped tongue, from which it separates at about 7 weeks. Postnatal anatomical development in humans involves a maturational descent in infancy (4 and 6 months of age). Contains lymphoid tissue (larynx-associated lymphoid tissue, LALT and Bronchus-associated lymphoid tissue, BALT).

eustacian tube - (auditory tube) A narrow canal connecting the middle ear space to the back of the oral cavity. The direct physical connection has two main functions to allow pressure equalization in, and fluid drainage from, the middle ear. In development, the canal is initially both horizontal and very narrow leading to poor drainage and easy blockage.

external auditory meatus - The canal from external ear (auricle) to the tympanic membrane (eardrum). Formed by the first pharyngeal cleft.

fetal period - (foetal period) In humans, the development week 9 to 36 is the fetal stage (second and third trimester) and during this time organs formed in the embryonic period continue to develop and the fetus grows in size and weight. The first 8 weeks of development is considered the embryonic period and is divided into 23 Carnegie stages based upon developmental milestones. Note when searching an alternate spelling "foetal".

fistula - An abnormal communication between 2 structures (organs, vessels, cavities) that do not normally connect.

fontanel - (fontanelle) A fibrous region between flat bones of developing skull. Have a role in birth allowing the cranial vault to flex and postnatally allow the skull to enlarge. In humans, there are six fontanels; an obvious anterior (bregmatic) and posterior (occipital) fontanels, as well the less noticeable lateral fontanels (two mastoid fontanels and two sphenoidal fontanels). A month or two after birth, the posterior and lateral fontanelles are lost, the anterior is not completely closed until about the 18 months.

foregut - The first of the three part/division (foregut - [M.htm#midgut midgut] - [H.htm#hindgut hindgut]) of the early forming gastrointestinal tract. The foregut runs from the buccopharyngeal membrane to the midgut and forms all the tract (esophagus and stomach) from the oral cavity to beneath the stomach. In addition, a ventral bifurcation of the foregut will also form the respiratory tract epithelium.

glottis - (Greek, = larynx) the boundary between pharynx to the larynx and consists of the vocal folds and their associated intervening space.

goitre - (goiter) The enlargement of thyroid gland due to a dietry deficiency of iodine, or thyroid hormone level abnormalities. Iodine is required to synthesise thyroid hormone which in turn is required for normal neurological development.

hard palate - he bony anterior portion of the palate formed by maxillary and palatine bones. The muscular posterior portion is called the soft palate.

head circumference - An ultrasound measurement of Head Circumference (HC) is used to determine fetal age and normal development (small/large/abnormal) parameters. Measured as an ellipse in a horizontal section at the level of the thalamus and the cavum septi pellucidi. It is one of the four typical ultrasound assessments of fetal size and age: [B.htm#biparietal_diameter Biparietal Diameter] (BPD), Head Circumference (HC), [A.htm#abdominal_circumference Abdominal Circumference] (AC), and [F.htm#femur_length Femur Length] (FL).

hypopharyngeal eminence - (hypobranchial eminence) An early embryonic structure in the developing head. A narrow midline mesodermal (mesenchymal) exension lying within the floor curve of the developing pharynx. Fusion of 3rd pharyngeal arches and precursor of root of tongue. Early developing thyroid cells also migrate into this structure as cords of cells.

hypophysis - (pituitary gland) Alternative name for the pituitary gland

incus - one of 3 bones of the middle ear (stapes-malleus-incus) converts mechanical vibration into fluid movement within cochlea. (More? Hearing Notes | Middle Ear)

internal auditory meatus - (internal acoustic meatus, IAM) An anatomical canal in which CN VII and CN VIII ganglia reside and pass through to the brainstem. This bony canal lies between the posterior surface of the petrous pyramid and the bony labyrinth within the dense petrous bone. Also associated clinically with the site where acoustic neuromas may occur.

(More? Inner Ear - Internal Auditory Meatus | Hearing Development - Inner Ear | Sensory Development - Hearing)

intramembranous ossification - The process of bone formation directly from a membrane, occurs in cranial vault (skull). The majority of skeleton formed by other process of bone formation on a cartilaginous template, endochondrial ossification. (More? Musculoskeletal Notes)

labyrinth - inner ear system of fluid-filled passages which provides the sense of balance (semicircular canals, vestibule). Named by analogy with the Greek mythology maze that imprisoned the Minotaur.

laryngeal webs - (congenital laryngeal webs) Laryngeal abnormality due to embryonic (week 10) incomplete recanalization of the laryngotracheal tube. Rare abnormality occuring mainly at the level of the vocal folds (glottis).

laryngotracheal groove - Early embryonic foregut developmental feature, forms on the anterior (ventral) wall of pharynx and gives rise to larynx, trachea, respiratory tree.

larynx - Site of the the vocal folds in the neck. Embryologically develops from the foregut with the lining derived from endoderm and the cartilage from pharyngeal arch 4 and 6. Beginning as a simple foregut groove, the [L.htm#laryngotracheal_groove laryngotracheal groove] which folds to form the laryngotracheal bud, then the larynx and trachea.

lingual - (Latin, lingua = tongue) Term used to describe structures and features related to the tongue: lingual papilla, lingual plate, lingual plexus, lingual thyroid nodule.

mandible - Term used to describe the lower jaw of the face, which forms from the lower part pharyngeal arch 1, the [#mandibular_process mandibular process]. The smaller upper part of pharyngeal arch 1 forms the two [#maxillary_process maxillary processes], which form the upper jaw. (More? Face Development | Face Abnormalities | Head Development)

mandibular process - In head and face development, lower part and majority of pharyngeal arch 1 which forms the lower jaw (mandible) of the face Smaller upper part of pharyngeal arch 1 are the [#maxillary_process maxillary processes]. (More? Face Development | Face Abnormalities | Head Development)

maxillary process - In head and face development, upper part of pharyngeal arch 1 which forms as a pair of small lateral swellings which contributes the upper jaw and forms the palatal shelves. Larger lower part of pharyngeal arch 1 is the [#mandibular_process mandibular process]. Associated abnormality is cleft palate/lip.

meatal plate - An ectodermal plug that temporarily blocks the external auditory meatus of the ear.

meatus - (Latin, meatus = a channel or way) An anatomical description of an opening or passageway (external auditory meatus, female urethral meatus). (More? Senses - Hearing)

meatoplasty - A surgical technique allowing reconstructive surgery of the external ear canal, often used to treat external meatus stenosis (More? Ear Abnormalities)

Meckel's cartilage - A temporary cartilage located in the first pharyngeal arch (mandibular component) that forms the template for formation of the mandible and middle ear bones. Named after Johann Friedrich Meckel, the Younger a German anatomist (1781 - 1833). (More? Head Notes | Who Named it? Johann Friedrich Meckel | PalaeosThe Gill Arches: Meckel's Cartilage )

medial epithelial seam - (MES) Embryonic structure formed by the fusion of the two palatal shelves, forming a two-layered medial edge epithelial seam, which is then lost with palate development. (More? Face - Abnormalities | Face Notes | | Head Notes | Medline Plus - Cleft Lip and Palate)

median eminence - (Latin, medialis = middle) A midline pouch or recess in the floor of the third ventricle and an extension of the hypothalamus together with the neural stalk forms the infundibular stem, which in turn together with the posterior lobe forms the pituitary neurohypophysis. (More? Endocrine - Hypothalamus | Endocrine - Pituitary )

mesenchyme - Term used to describe the cellular organisation of undifferentiated embryonic connective tissue . Mesenchymal tissue is mainly derived from mesoderm and neural crest, which will form most of the adult connective tissues. This connective tissue organization contrasts with the other main form of cellular organization, epithelial tissue.

mesethmoid cartilage - The ventral component of the nasal capsule. In the chicken embryo, it is induced by sonic hedgehog (Shh) expression from endoderm (endoderm zone I).

mesoderm - The middle layer of the 3 germ cell layers of the embryo. Mesoderm outside the embryo and covering the amnion, yolk and chorion sacs is extraembryonic mesoderm.

metopic suture - A skull fibrous joint, cranial suture between adjacent developing bones of the skull. This suture begins at nose and runs superiorly to meet sagittal suture and fuses in early childhood before all other cranial sutures. Premature fusion (synostosis) of metopic suture causes Trigoncephaly (wedge skull). (More? Skull Notes | Head Notes)

microtia - The condition of an abnormally small external ear.

midbrain flexure - (pontine flexure) [P.htm#pontine_flexure pontine flexure] The middle curvature that forms in the early rapidly growing neural tube.

myogenesis - The process of muscle cell development or formation. In skeletal muscle the cellular sequence is: myoblast, myotube and myofibre.

neural crest - A cell region at edge of neural plate, then atop the neural folds, that remains outside and initially dorsal to the neural tube when it forms. These paired dorsal lateral streaks of cells migrate throughout the embryo and can differentiate into many different cell types (= pluripotential). Those that remain on the dorsal neural tube form the sensory spinal ganglia (DRG), those that migrate ventrally form the sympatheitic ganglia. Neural crest cells also migrate into the somites and regions throught the entire embryo.

olfactory - Refers to the sense of smell.

olfactory epithelium - The specialised sensory epithelium that lines the nasal cavity associated with smell. Some cells within the adult epithelium remain as stem cells which can be isolated and purified.

oropharynx - The second portion of the pharynx (throat) that is posterior to the oral cavity. The other pharynx regions are the nasopharynx and laryngopharynx (hypopharynx).

otolith - A calcium carbonate concretion in the vestibular portion of inner ear, involved with balance.

oxycephaly - (oxycephalus, "tower skull")Skull defect resulting from premature coronal suture synostosis. One of several skull deformities (scaphocephaly, oxycephaly, plagiocephaly, trigoncephaly) caused by premature fusion (synostosis) of different developing skull sutures.

palate - The roof of the mouth (oral cavity) a structure which separates the oral from the nasal cavity. Develops as two lateral palatal shelves which grow and fuse in the midline. Initally a primary palate forms with fusion of the maxillary processes with the nasal processes in early face formation. Later the secondary palate forms the anterior [H.htm#hard_palate hard palate] which will ossify and separate the oral and nasal cavities. The posterior part of the palate is called the soft palate (velum, muscular palate) and contains no bone. Abnormalities palatal shelf fusion can lead to [C.htm#cleft_palate cleft palate].

palatogenesis - The process of palate formation.

paranasal sinuses - Air-filled cavities surrounding the nasal cavity and open into it, which combine in function to: reduce skull weight, produce mucus, and act as resonating chambers affecting voice quality. Located within in the frontal, maxilae, ethmoid, and sphenoid bones with the same name as the bones in which they are located.

pars - (Latin, pars = part of) Anatomical term describing something as part of an organ or tissue.

pharyngeal arch - (branchial arches, Greek, branchial = gill) These are a series of externally visible anterior tissue bands lying under the early brain that give rise to the structures of the head and neck. In humans, five arches form (1,2,3,4 and 6) but only four are externally visible on the embryo. Each arch has initially identical structures: an internal endodermal pouch, a mesenchymal (mesoderm and neural crest) core, a membrane (endoderm and ectoderm) and external cleft (ectoderm). Each arch mesenchymal core also contains similar components: blood vessel, nerve, muscular, cartilage. Each arch though initially formed from similar components will differentiate to form different head and neck structures.

pharyngeal arch artery - Each early developing pharyngeal arch contains a lateral pair of arteries arising from the aortic sac, above the heart, and running into the dorsal aorta. later in development these arch arteries are extensively remodelled to form specific components of the vascular system. Pharyngeal Arch 1 arteries are mainly lost and forms part of maxillary artery. Pharyngeal Arch 2 arteries remains to form the stapedial arteries. Pharyngeal Arch 3 arteries forms the common carotid arteries, internal carotid arteries in the neck. Pharyngeal Arch 4 arteries will form part of aortic arch (left arch artery) and part right subclavian artery (right arch artery) Pharyngeal Arch 6 arteries form part of left pulmonary artery (left arch artery) and part of right pulmonary artery (right arch artery).

pharyngeal arch cartilage - Each early developing pharyngeal arch contains a horseshoe shaped band of cartilage that acts as a template and contributes to the development of head and neck bony and cartilagenous features, including the middle ear bones. Pharyngeal Arch 1 cartilage (Meckel’s cartilage) dorsal ends form malleus and incus midpart forms ligaments (ant. malleus, sphenomandibular) ventral part forms mandible template. Pharyngeal Arch 2 cartilage (Reichert’s cartilage) dorsal ends form stapes and Temporal bone styloid process, ventral part ossifies to form hyoid bone components, lesser cornu and superior body. Pharyngeal Arch 3 cartilage forms hyoid components, greater cornu and inferior part of hyoid. Pharyngeal Arch 4 and 6 cartilage forms laryngeal cartilages except epiglottis (from hypobranchial eminence).

pharyngeal arch nerve - Each early developing pharyngeal arch contains the developing cranial nerves, as a pair, within the arch mesenchyme. Each cranial nerve is numbered (roman numeral) in rostrocaudal sequence and also has a specific name. The cranial nerve within each arch often relates to the other structures formed from taht arch. Pharyngeal Arch 1 contains the trigeminal nerve (CN V, cranial nerve 5). Pharyngeal Arch 2 contains the facial nerve (CN VII, cranial nerve 7). Pharyngeal Arch 3 contains the glossopharyngeal nerve (CN IX, cranial nerve 9) Pharyngeal Arch 4 and 6 contains the Vagus (CN X cranial nerve 10), forming the adult superior laryngeal and recurrent laryngeal branches.

pharyngeal arch pouch - An out-pocketing of the endoderm lined pharynx occurring between each developing pharyngeal arch. Each of the pharyngeal arch pouches contributes different components of the head and neck, either cavities or endocrine tissues. Pharyngeal Arch 1 pouch elongates to form tubotympanic recess tympanic cavity, mastoid antrum and auditory tube (Eustachian tube). Pharyngeal Arch 2 pouch forms the tonsillar sinus and is later mostly oblierated by palatine tonsil. Pharyngeal Arch 3 pouch forms the inferior parathyroid and thymus. Pharyngeal Arch 4 pouch forms the superior parathyroid, parafollicular cells of Thyroid.

pharynx - (throat) Forms the initial segment of the upper respiratory tract divided anatomically into three regions: nasopharynx, oropharynx, and laryngopharynx (hypopharynx). Anatomically extends from the base of the skull to the level of the sixth cervical vertebra.

pharynx - uppermost end of gastrointestinal and respiratory tract, in the embryo beginning at the buccopharyngeal membrane and forms a major arched cavity within the phrayngeal arches.

placode - (Greek, plax = plate, eidos = shape or form) A surface ectoderm thickening seen in the early embryo head region. Each pair of placodes will contribute a different component of each sensory system (otic placode, optic placode, nasal placode).

Rathke's pouch - An ectodermal fold in roof of pharynx forming anterior pituitary (adenohypophysis) and pars intermedia. Named after German embryologist and anatomist Martin Heinrich Rathke (1793 -1860).

Reichert's cartilage - Neural crest forming the cartilage band of the second pharyngeal arch.

rhombomere - A segmentation of the hindbrain (rhombencephalon) reflects segemental (rostro/caudal) expresion of Hox gene.

scalp vascular plexus - A vascular feature visible on the head surface from Carnegie stage 20 (day 50).

scaphocephalus - One of several skull deformities (scaphocephaly, oxycephaly, plagiocephaly, trigoncephaly) caused by premature fusion (synostosis) of different developing skull sutures. Scaphocephaly results from premature sagittal suture synostosis.

sella turcica - (Latin sella = saddle, turcica = Turkish) refers to the shape of the sphenoid bone in which the pituitary gland resides (pituitary fossa).

Sessel's pouch - In early head development, an endodermal bud underlying the nasofrontal bud will form Sessel's pouch which later degenerates. In the chick embryo, this structure patterns first the nasal septum and later the nasal capsule, the ethmoid bone, and the upper beak.

soft palate - (velum, muscular palate) The muscular posterior portion of the palate forming the roof of the oral cavity. The bony anterior portion of the palate is called the hard palate, formed by maxillary and palatine bones.

stomadeum - (stomadeum) A ventral surface depression on the early embryo head surrounding the [B.htm#buccopharyngeal_membrane buccopharyngeal membrane], which lies at the floor of this depression. This surface depression lies between the maxillary and mandibular components of the first pharyngeal arch.

tensor veli palatini - A muscle which functions to open the auditory tube by pulling its lateral wall laterally and inferiorly.

teratogen - (Greek, teraton = monster) Any agent that causes a structural abnormality following exposure during pregnancy. The overall effect depends on dosage and time of exposure. Absolute risk - the rate of occurrence of an abnormal phenotype among individuals exposed to the agent. (e.g. fetal alcohol syndrome) Relative risk - the ratio of the rate of the condition among the exposed and the non-exposed. (e.g. smokers risk of having a low birth weight baby compared to non-smokers) A high relative risk may indicate a low absolute risk if the condition is rare.

thyroid - (Greek, thyreos = sheild , eidos = form) endocrine gland located in the neck, the origin of the name reflects the organs anatomical structure. In the fetus, the thyroid gland has a role in neurological development.

thyroiditis - (Greek, thyreos = sheild , eidos = form) An inflammatory process affecting the thyroid epithelium.

umami - An historical Japanese word describing the taste in seaweed, used to describe the taste sensation of "savoury". Stimulated by the amino acid glutamate and monosodium glutamate.

vagus - (Latin, vagus = wandering) cranial nerve X (CN X) A mixed nerve that leaves the head and neck to innervate gastrointestinal tract (pharynx, esophagus, stomach) respiratory tract (larynx, lungs), cardiac (heart) and abdominal viscera. This mixed nerve has sensory, motor and autonomic functions of viscera (glands, digestion, heart rate).

vellus hair - short hairs seen on newborn infant, these hairs are only a centimetre or two long and contain little or no pigment. Follicles that produce them do not have sebaceous glands and never produce any other kind of hairs.

vitreous humor - A gel-like mass located in the vitreous (posterior) chamber of the eye. In development the vitreous also contains the hyloid blood vessels.

vocal folds - Folds occuring in the larynx used in generating sounds required for speech.