THE PYRAMIDAL TRACT 529 



present in the area which the tract occupies, were of different 

 diameters and closely packed. Even in the monkey the non- 

 medullated fibers of the tract outnumber those which are 

 medullated. 



The average size of the medullated fibers was less than in the 

 cords of the cat or rabbit, but greater than in the cords of the rat 

 and guinea-pig. The largest found measured 11 .95 ^ in diameter, 

 while the majority of these fibers measured from 4.8 ju to 9.6 ^u 

 in diameter (table 1). 



SUMMARY 



1. The pyramidal tract of the higher mammals contains both 

 medullated and non-meduUated fibers. 



2. In the mole the tract is almost completely non-medullated. 

 In the rat it is very imperfectly medullated. 



3. The tracts decussate in the medulla oblongata in all animals 

 except the mole, where a decussation is suggested throughout 

 the course of the tract in the cervical part of the cord. 



4. The tracts may lie in any funiculus of the cord. In the 

 mouse, rat and guinea-pig this tract lies in the posterior funiculus; 

 in the rabbit and the carnivora, in the lateral funiculus; and in 

 the ground-mole, in the anterior funiculus. 



5. They traverse the entire cord in all animals studied except 

 in the mole where they terminate with the cervical cord. 



6. The imperfect meduUation of the pyramidal tract in these 

 animals is of interest in connection with its late medullation in 

 man. The degree of medullation in man can not be studied, 

 since no satisfactory preparations are available. 



BIBLIOGRAPHY 



Bechterew, W. 1890 Ueber die verschiedenen Lagen und Dimensionen der 



Pyramidenbahnen beim Monschen und den Thieren. Neurol. Central., 



Bd. 9, S. 738. 

 BiACH, P. 1907 Das Riickenmark der Ungulaten. Arbeit aus dem Neuro- 



logisches Institut aus der Wienischen Universitat, Bd. 16, S. 487. 

 BiscHOFF, E. 1900 Beitrag zur Anatomie des Igelhirnes. Anat. Anz., Bd. 18, 



S. 348. 



