_a_, head-fold of amnion. _aa_, anterior appendage. _ac_, anterior cardinal vein. _al_, allantois. _an_, anterior nares. _ao_, aorta. _aop_, area opaca. _ap_, area pellucida. _ar_, aortic arch. _au_, auricle. _b_, bulbus arteriosus. _bc_, body cavity. _blp_, blastopore. _bp_, basilar plate. _bv_, blood-vessel. _c_, centrum of vertebra. _ca_, caudal artery. _ch_, cerebral hemisphere. _cl_, cloaca. _cn_, cranial nerve. _cp_, posterior choroid plexus. _cv_, cardinal veins. _dc_, ductus Cuvieri. _e_, eye. _ec_, ectoderm. _ec′_, thickening of ectoderm, _en_, entoderm. _en′_, endocardium. _ent_, enteron. _ep_, epidermal layer of ectoderm. _epi_, paraphysis. _es_, embryonic shield. _f_, fronto-nasal process. _fb_, forebrain. _fg_, foregut. _g¹⁻⁵_, gill clefts. _gf¹⁻⁶_, gill folds. _gl_, glomerulus. _h_, head-fold. _hb_, hindbrain. _ht_, heart. _i_, intestine. _i′_, stomach. _in_, infundibulum. _ir_, iris. _it_, iter. _k_, kidney (metanephros). _l_, remains of groove between secondary folds. _la_, larynx (cartilages of). _li_, liver. _ll_, lower lid of eye. _ln_, lens. _lr_, inferior rectus muscle of eye. _lu_, lungs. _lv_, lens vesicle. _m_, mouth. _ma_, manus. _mb_, midbrain. _mc_, medullary canal. _me′_, tip end of medullary canal. _md_, mandibular fold. _mes_, mesoderm. _mes′_, myocardium. _mf_, medullary fold. _mg_, medullary groove. _mk_, Meckel’s cartilage. _mp_, muscle plate. _ms_, mesentery. _mv_, meatus venosus. _mx_, maxillary fold. _myc_, myocœl. _n_, nasal invagination or cavity. _na_, neural arch of vertebra. _nc_, neurenteric canal. _nl_, nervous layer of ectoderm. _nt_, notochord. _o_, ear vesicle. _oc_, optic cup. _oe_, œsophagus. _on_, optic nerve. _os_, optic stalk. _ov_, optic vesicle. _p_, pituitary body. _pa_, posterior appendage. _pan_, pancreas. _pc_, posterior cardinal vein. _pe_, pes. _pg_, primitive groove. _ph_, pharynx. _pl_, pelvis. _pn_, posterior nares. _pr_, pericardial cavity. _ps_, primitive streak. _pt_, pecten. _rt_, retina. _s_, somites. _sc_, spinal cord. _se_, sphenethmoid cartilage. _sf_, secondary fold. _sg_, spinal ganglion. _sm_, splanchnic mesoblast. _sn_, spinal nerve. _so_, somatic mesoblast. _st_, stomodæum. _sy_, sympathetic nervous system. _t_, tail. _ta_, trachea. _tg_, thyroid gland. _th_, thickening and posterior limit of _sf_. _tn_, tongue. _to_, tooth anlage. _tr_, truncus arteriosus. _tv_, third ventricle of brain. _tv′_, third ventricle of brain. _u_, umbilical stalk. _ul_, upper lid of eye. _ur_, superior rectus muscle of eye. _v′-″-‴_, first, second, and third cerebral vesicles. _va_, vascular area. _vm_, vitelline membrane. _vn_, ventricle of heart. _vv_, vitelline blood-vessels. _wd_, Wolffian duct. _wdo_, opening of Wolffian duct.