22 ABNORMAL CONDITIONS OF THE AXIS. 



The external generative organs of the other side are 

 very ill-formed, and are only connected with the internal 

 organs by the right round ligament of the uterus of the 

 lower foetus. There is no indication of either urethra, 

 vagina, or anus on this side. There is a small swelling, 

 about as large as a pea, at the anterior extremity of the 

 left labium. 



101. Human female twins, about the sixth month of gestation, 

 united by opisthozygosis. The second foetus is exces- 

 sively malformed, and possesses neither heart nor brain. 



The axes are united near the lower part of the dorsal 

 vertebrae by ordinary intervertebral cartilage and liga- 

 ments, exactly like those between the consecutive verte- 

 brae. The remainder of both vertebral columns is want- 

 ing as far as the sacral vertebras. There is a large sacrum 

 on the left side, placed at right angles to and behind the 

 united vertebral columns. The sacrum on the right side 

 is very defective, consisting of a mere ring of bone articu- 

 lated with the base of the left sacrum by cartilage and 

 ligament. 



The neural arches of the vertebrae are open behind at 

 the point of union between the sacra and vertebral 

 columns. The laminae of both columns form a conti- 

 nuous series with those on the adjacent sides of the sacrum 

 on the left side, and of the rudimentary sacrum on the 

 right ; a large lozenge-shaped opening is thus left in the 

 neural canal. 



The neural canal of the sacrum is continuous with that 

 of the vertebrae, and this makes a sharp bend backwards 

 from either axis to meet the sacral neural canal. 



The following facts were recorded by Drs. Marcet, 

 Roget, and Mr. Lawrence from an examination made 

 when the foetus first arrived in England : " The inter- 

 val between the lamina of the vertebra was occupied by 

 a strong membrane ; on the division of this, the medulla 

 spinalis was seen running across from one spine to the 

 other, and distributing its nerves laterally to the two 

 lateral pelves/' 



From a careful consideration of the above conditions, it appears 

 that the axes of two embryos came into contact at a very early 

 period of development, so that the neural cords arid the proto- 



