6 ABNORMAL CONDITIONS OF THE AXIS. 



27. A small English Snake with two heads. 



Presented by W. White Cooper, Esq., 1872. 



B. Posterior Dichotomy. 



There is no true case of congenital posterior dichotomy in 

 Reptiles in the Collection. The following specimen probably 

 represents an acquired condition, the result of injury and the 

 well-known powers of repair possessed by these animals. 



28. A Lizard in which a portion of the extremity of the tail is 



double. Hunterian. 



Subseries V. IN BIRDS, 



Subclass I. Dichotomy. 



A. Anterior Dichotomy. 



29. A foetal Duck with two heads and necks ; the dorsal vertebrae, 



the trunk, and its appendages are single. 



Hunterian. 



30. A similar foetal Turkey with the skull and vertebral canal 



open from arrested closure of the neural arches, 



Presented by Lady Northampton. 



31. A similar fo3tal Fowl, in which the neural arches of the head 



are undeveloped. The brain-membranes are exposed. 



Presented by Sir W. Elizard. 



32. A similar foetal Chick with fusion of the heads, so that the 



approximate eyes have coalesced into a single organ. The 

 neural arches of the head are undeveloped, and the brains 

 are exposed. The spinal cord is deficient, the vertebral 

 canal containing its membranes only. . Hunterian. 



B. Posterior Dichotomy. 



33. A Chick with the posterior half of the cerebro-spinal axis 



double. There are four legs, but the wings are two in 

 number. The abdominal parietes are deficient, and the 

 neural laminae are undeveloped in the cervical region. 

 There is a slight notch in the upper mandible, as if a 

 tendency to superior dichotomy had likewise existed. 



Hunterian. 



34. A Duckling with posterior dichotomy of the greater part of 



