OP ARTS AifD SCIENCES. 97 



II. 



CONTRIBUTIONS FROM THE ZOOLOGICAL LABORATORY 



OF THE MUSEUM OF COMPARATIVE ZOOLOGY 



AT HARVARD COLLEGE. 



No. L— ON THE DEVELOPMENT OF THE POSTERIOR 

 FISSURE OF THE SPINAL CORD, AND THE REDUC- 

 TION OF THE CENTRAL CANAL, IN THE PIG* 



By William Barnes. 



Presented June 13, 1S83, by Alexander Agassiz. 



It is well known that the anterior and posterior fissures of the spinal 

 cord are not produced in the same manner. While the formation of 

 the anterior fissure results from a comparatively simple process of 

 growth and enlargement in the region of the anterior horns, the pro- 

 duction of the posterior fissure appears to be dependent on more com- 

 plicated changes. More or less intimately connected with its formation 

 is the disappearance of a portion of the original lumen of the neural 

 tube. Whether, however, the posterior fissure is "a part of the origi- 

 nal neural canal separated from the rest of the cavity by a median 

 coalescence of the side walls," as claimed by Foster and Balfour ; or 

 whether the atrophy of a portion of the canal is only a necessary ante- 

 cedent to the formation of the fissure ; or whether, finally, its oblitera- 

 tion may be considered as causally connected with the appearance of 

 the fissure, — appear still to be questions which have not received their 

 definite answer.f 



It was with a view to gaining additional information on these points 

 that the following investigations on the pig were undertaken. 



Literature. 

 Clarke, J. L. 



'62. Researches on the Development of the Spinal Cord in Man, Mammalia, 

 and Birds. Philos. Trans. Royal Soc. London, 1862, pp. 911-938, PI. 

 XLV.-XLVIII. 



* The following investigations were made in the Embryological Laboratory of 

 the Museum, under the supervision of Dr. E. L. Mark. 



t Balfour ('81, p. 344) says, " The exact mode of its formation appears to me 

 to be still involved in some obscurity." 

 VOL. XIX. (n. s. XI.) 7 



