Fig.182. Median longitudinal section of the tail of a human embryo, two-thirds of an inch long. Fig. 182—Median longitudinal section of the tail of a human embryo, two-thirds of an inch long. (From _Ross Granville Harrison._) _Med_ medullary tube, _Ca.fil_ caudal filament, _ch_ chorda, _ao_ caudal artery, _V.c.i_ caudal vein, _an_ anus, _S.ug_ sinus urogenitalis.
Fig.183. Human embryo, four weeks old, opened on the ventral side. Fig. 183—Human embryo, four weeks old, opened on the ventral side. Ventral and dorsal walls are cut away, so as to show the contents of the pectoral and abdominal cavities. All the appendages are also removed (amnion, allantois, yelk-sac), and the middle part of the gut. _n_ eye, _3_ nose, _4_ upper jaw, _5_ lower jaw, _6_ second, _6″_ third gill-arch, _ov_ heart (_o_ right, _o′_ left auricle; _v_ right, _v′_ left ventricle), _b_ origin of the aorta, _f_ liver (_u_ umbilical vein), _e_ gut (with vitelline artery, cut off at _a′_), _j′_ vitelline vein, _m_ primitive kidneys, _t_ rudimentary sexual glands, _ r_ terminal gut (cut off at the mesentery _z_), _n_ umbilical artery, _u_ umbilical vein, _9_ fore-leg, _ 9′_ hind-leg. (From _Coste._)
Human embryo, five weeks old, opened from the ventral side. Fig. 184—Human embryo, five weeks old, opened from the ventral side (as in Fig. 183). Breast and belly-wall and liver are removed. _3_ outer nasal process, _4_ upper jaw, _5_ lower jaw, _z_ tongue, _v_ right, _v′_ left ventricle of heart, _o′_ left auricle, _b_ origin of aorta, _b′, b″, b‴_ first, second, and third aorta-arches, _c, c′, c″_ vena cava, _ae_ lungs (_y_ pulmonary artery), _e_ stomach, _m_ primitive kidneys (_j_ left vitelline vein, _s_ cystic vein, _a_ right vitelline artery, _n_ umbilical artery, _u_ umbilical vein), _ x_ vitelline duct, _i_ rectum, _8_ tail, _9_ fore-leg, _9′_ hind-leg. (From _Coste._)
It sometimes happens that we find even external relics of this tail growing. According to the illustrated works of Surgeon-General Bernhard Ornstein, of Greece, these tailed men are not uncommon; it is not impossible that they gave rise to the ancient fables of the satyrs. A great number of such cases are given by Max Bartels in his essay on “Tailed Men” (1884, in the _Archiv für Anthropologie,_ Band XV), and critically examined. These atavistic human tails are often mobile; sometimes they contain only muscles and fat, sometimes also rudiments of caudal vertebræ. They have a length of eight to ten inches and more. Granville Harrison has very carefully studied one of these cases of “pigtail,” which he removed by operation from a six months old child in 1901. The tail moved briskly when the child cried or was excited, and was drawn up when at rest.