28 ABNORMAL CONDITIONS OF THE AXIS. 



of an auricle and ventricle. The ventricle gives an aorta 

 to either foetus, and is fused with the base of the ventricle 

 of the lower heart. The lower heart has two auricles. 

 The apices of both ventricles are turned towards the front 

 of the preparation. . The specimen was so brittle that the 

 exact distribution of the vessels could not be made out. 



c. Pleuropagus, Forster. 



Syn. Dicephalus, Gurlt. 



Monstres doubles Sysomiens, Geoff. 



In Pleuropagus two axes are adherent side by side. Such ab- 

 normal twins have hitherto been called dicephalus, from their 

 external resemblance to dichotomous conditions of the anterior 

 extremity of the axis. In these forms, however, the whole axis 

 is double. They are transitional between anterior dichotomy 

 and parazygosis. The median limbs are frequently fused toge- 

 ther, and are sometimes reduced to mere tubercles. 



118. A Human pleuropagous twin-birth, about the end of the third 



month (length 4| inches), with the mesial (posterior) arms 

 and legs fused together as far as the carpus and tarsus. 

 It is apparently female, but the organs of generation are 

 very imperfectly formed. This specimen is transitional 

 between thoracopagus and the more marked forms of 

 pleuropagus. Purchased, 1870. 



119. Human male pleuropagous twins. The median (posterior) 



arms form a mei*e tubercle upon the back. There are no 

 median legs, although there are two axes even to the ex- 

 tremity of the sacrum. The median innominate bones 

 are absent. 



120. The bones and ligaments of the united mesial arms of an 



exactly similar foetus. 



A small portion of the broad sternum, formed by the 

 union of two sterna, supports a pair of clavicles closely 

 pressed together; distinct and flattened in front, but 

 united behind. These articulate with the two acromia of 

 a very remarkable double scapula, and are also united 

 with the glenoid cavity by ligament, a piece of cartilage 

 intervening. The scapula is symmetrical, and presents 

 two spines and two acromia ; one of the latter has been 

 cut through and turned back to show the manner in which 



