XX11 INTEODUCTION. 



become widely separated by the manner in which the ilia 

 and sacrum supported the weight of the trunk. 



With regard to the nature of the origin of arrest nothing 

 is known positively. Like all malformations, some forms 

 appear closely allied to variations, some to diseases. In 

 arrest, however, the variations, if they be such, take the 

 form of reversions. This may be more apparent than real ; 

 but in some Ceases, where growth continues and evolution 

 does not, it appears as if the parts are actually developed in 

 conformity with an anterior type rather than simply arrested 

 in their formation. Bilocularity of the human uterus, the 

 formation of uterine cornua, enlargement of the clitoris, 

 development of the uterus masculinus, hypospadias, the 

 formation of a cloaca, webbing of the fingers, arrest of the 

 ventricular septum of the heart, and the persistence of a 

 spiracle uniting the pharynx and auditory meatus are ex- 

 amples of this kind. 



Class VI. DISEASE. 



The last class of malformations consists of intra-uterine 

 diseases and their results. The most marked forms are 

 those of spinal and appendicular deformity, and dropsy of 

 the central canal of the nervous system, giving rise to 

 hydrocephalus, epicephalocele, spina bifida, &c. 



It will be observed that no class has been formed for 

 malformations from excess of development ; for it may well 

 be doubted if any such exist, unless under the forms of 

 variation or duplicity. 



There are, however, some cases which might possibly be 

 considered as the result of excess in the developmental 

 process ; although, without more evidence, it appears inju- 

 dicious to erect a class which all observations tend to render 

 more and more hypothetical in its nature. Certain fishes, 

 for instance, occasionally exhibit a very remarkable form of 

 hermaphrodism in which a portion of an ovary is developed 

 as a testis, whilst the remainder becomes a perfect ovary. 



