| matrix metalloproteinases (MMPs) | a family of proteolytic enzymes which act in concert with inhibitors to model extracellular matrix |
| morphogenesis | differentiation of cells and tissues in the early embryo which results in establishing the form and structure of the various organs and parts of the body |
| nasal placodes | placodes are thickenings of ectoderm which go on to form sensory structures. Nasal placodes form the sensory olfactory epithelium of the nose |
| mesenchyme | the undifferentiated tissue of the early embryo that forms from mesoderm and neural crest tissue |
| mesoderm | the middle germ layer of the early embryo which gives rise to cartilage, muscle, bone, blood, kidneys, gonads and connective tissue |
| neural crest | sometimes referred to as the fourth germ layer, neural crest migrates throughout the embryo and has many derivatives, paricularly in the peripheral nervous system and in the head and neck |
| polymorphisms | conditions where a chromosome or a gene occur in more than one form |
| premaxilla/premaxillary segment | the bony parts in the adult which formed from the intermaxillary segment in the embryo. It refers to the area of hard palate anterior to the incisive foramen, the central upper jaw and associated alveolar process bearing the four upper incisors |
| proband | the first individual studied in an investigation of several related patients with an inherited or familial disorder |
| prochordal plate | the area at the cranial end of the early embryo where ectoderm and endoderm are tightly apposed. Mesoderm does not penetrate here. This represents the future mouth area of the embryo |
| pterygopalatine ganglion | a parasympathetic ganglion (collection of cell bodies) located in the pterygopalatine fossa between the palatine and sphenoid bones of the skull. Besides parasympathetic fibres, the maxillary division (V2) of the trigeminal nerve passes to it and it then sends nerves to the palate and nasal cavity |
| stomodeum | the site of the embryonic mouth. It is a depression lined with ectoderm and in its base is the temporary buccopharyngeal membane which separates the mouth from the developing pharynx |
| thalidomide | drug: formerly used as a sedative, it was found to cause severe fetal abnormalities if taken in the first trimester. It has now been withdrawn |
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