33^ The Alligator and Its Allies 



lu, lungs. 



Iv, 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, myocoel. 



n, nasal invagination or cavity. 



na, neural arch of vertebra. 



nc, neurenteric canal. 



nl, nervous layer of ectoderm. 



nt, notochord. 



0, ear vesicle. 



oc, optic cup. 



oe, oesophagus. 



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. 



pi, pelvis. 



pn, posterior nares. 



pr, pericardial cavity. 



ps, primitive streak. . 



pt, pecten. 



ri, 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, stomodagum. 



sy, sympathetic nervous system. 



/, tail. 



ta, trachea. 



tg, thyroid gland. 



th, thickening and posterior limit 



oi 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. 

 w, vitelline blood-vessels. 

 wd, Wolffian duct. 

 wdo, opening of Wolffian duct. 

 wr, Wolffian ridge. 

 wt, Wolffian tubules. 

 y, yolk. 



EXPLANATION OP FIGURES 1-26 ON PLATES VI.-XXVIII. 



All of the figures, with the exception of the photographs and those 

 copied by permission from S. F. Clarke, weredrawn nndaro. earner alucida. 



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