DUPLICITY. 23 



vertebrae in the dorsal regions were developed in a continuous 

 series ; and the caudal extremities of the axes became displaced 

 and partially absorbed, so that the axial portion of the sacrum 

 has been developed from the remains of one of these displaced axes. 

 The neural arches appear to have followed the same law of deve- 

 lopment as the visceral arches at the point of union between the 

 foetuses, those of the one axis tending to unite with those of the 

 other instead of with their fellows. 



A comparison with other specimens of a similar malformation 

 renders its probable that the upper pair of legs and the correspond- 

 ing pelvic bones were developed from the visceral laminae of the 

 upper, and the lower pair from those of the lower foetus. 



The thoracic viscera of the upper foetus are normal. The aorta 

 in the abdomen turns off to the left pelvis and gives off a pair of 

 large hypogastric arteries, of which the upper is the larger. At 

 the point where the aorta turns off to the left it gives origin to two 

 large vessels : one runs straight into the thorax of the lower foetus 

 and terminates in two innominate arteries, the other supplies the 

 right pelvis and lower limbs. 



The whole of the anterior walls of both foetuses are extremely de- 

 fective. The ribs of the lower foetus are developed behind only. A 

 slip of muscle crosses its body -cavity from tjie left axilla to the right 

 pubis. Its thorax was chiefly occupied by a large sac, the greater part 

 of which has been removed with the viscera, and is seen in the next 

 preparation. This sac communicated with the intestines above and 

 with the mouth below. It is referred to in M. Maunoir's original 

 description of this monster (Med.-Chir. Trans, vol. vii. p. 257) as a 

 " kind of cloaca," of which he says, " On opening the cloaca it was 

 found to contain the rudiments of a lower jaw and of a tongue, which 

 were immersed in meconium, with which the cavity was filled." 

 The cranial and facial bones are only represented, in the inferior 

 head, by irregular masses of cartilage. There is a very rudimen- 

 tary and misshapen external ear. The brain was represented by a 

 large cyst filled with blood, a condition usual in anencephalic con- 

 ditions : this was removed before the foetus was sent to England. 



The following history is recorded (Med.-Chir. Trans. I.e.}: 

 " A girl of 16 or 17 gave birth to this foetus in Geneva ; it lived 

 a few minutes. There was no difficulty in the labour ; the perfect 

 head was born last." 



Presented by the Medico- Chirurgical Society, 1816. 



102. The abdominal viscera of the same, except the liver, and 

 the kidneys which were contained in the left pelvic por- 

 tion of the twin-birth ; these parts had been removed. 



