The Nervous System 



289 



embryos form which are wholly separate, but have common en- 

 velops and umbilic cords. In the cow not rarely we find one of 

 the two embryos so aberrant in form as to constitute a well nigh 

 shapeless mass like Figs. 26 and 27, known as artiorphus, 

 acardia, or a "mole." 



Fig. 26. ":\IoLK," OR .A.CARDIA. From Cow. 

 M, Muzzle. SM, SM, Superior maxilla, showing white denticles. 

 IM, IM, Inferior maxilla showing denticular masses (grinders). 

 BM, Buccal mucosa showing papilla. 

 T, Tongue. I, Incisors. 

 One-half size. 



The fusion of the lips of the neural canal may become inter- 

 rupted at various points and the canal may remain open even to 

 the time of birth, to constitute spinal bifida. An instance of 

 this occurring in the dorsal region (dorsal .spinal bifida) is shown 

 in Fig. 28, in which the superior wall of the spinal canal is want- 

 ing from the dorsal region, backward. A similar persistence of 

 the neural groove may occur at any point in its entire length, 

 producing cervical, dorsal, lumbar or .sacral .spinal bifida, accord- 

 ing to location. 

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