ARREST OF DEVELOPMENT. XXI 



fusion results, with the absence of the parts which nor- 

 mally intervene. The axis of the skull may fail to a greater 

 or less extent, a condition accompanied by fusion of the 

 eyes (cyclopia) and absence of the median structures of the 

 nose, and usually accompanied by an arrested condition of 

 the brain, in which, although growth has continued, evolu- 

 tion has not; it probably arises from defective nutrition 

 or atrophy of the axis of the skull, and may be considered 

 as the result of very early embryonic disease. 



The various forms of facial fusion (Cyclopia, Ethmocepha- 

 lus, &c.), certain defective conditions of the limbs (Perome- 

 lid), fusion of the limbs (Sympodid], and deficiencies of other 

 parts are also probably of this kind. 



IV. In the fourth form of arrest, differentiation fails at an 

 early period ; this is seen most frequently in the intercostal 

 spaces, a complete layer of bone being formed in the place 

 of intercostal muscles between an adjacent pair of ribs. It 

 usually accompanies severe forms of arrest in other parts. 

 Sometimes no muscles exist, the whole body being formed 

 of dense connective tissue, containing bones and cartilages. 

 Other examples of this kind of arrest, which might fairly 

 be called histological, occur. 



V. Lastly, the heart may undergo an arrest of develop- 

 ment and atrophy at a very early period, so that ,an acardiac 

 foetus results. Such malformations always exhibit great 

 histological arrest ; many of the organs remain in an em- 

 bryonic condition, although they may increase in size. 

 Some parts become so altered that they can scarcely be 

 recognized. The head is usually completely absent, or it 

 consists of a mere bony cyst. 



Functionally active organs always undergo considerable 

 after modification whenever their development has been 

 arrested : this is especially seen in the heart. Other parts 

 exhibit the conditions in a less degree. The pelvis No. 424 

 is a good example of this phenomenon : the pubic bones 

 have been arrested in their growth in consequence of their 

 taking no part in the support of the body, and they have 



