102 CARNEGIE INSTITUTION OF WASHINGTON. 



area resembling the septal nucleus of lower vertebrates. Dorsally 

 it is continuous with the fascia dentata and is separated from the 

 latter and from the fissura by a ventricular sulcus. The anterior 

 conomissure appears in embryos about 39 mm. long, the dorsal com- 

 missure in embryos about 60 mm. long. The course of development 

 of the medial olfactory cortex is as extensive in man, therefore, as in 

 other vertebrates. 



Professor Kanae Kunitomo, who spent some time with us last 

 year, studying certain features in the development of the tail and 

 of the caudal end of the spinal cord in human embryos, has published 

 the results of his investigations. His study is based upon profile 

 reconstructions of the caudal region in 44 human embryos, ranging 

 i n length from 4 to 125 mm. and representing the entire period of 

 development of the caudal appendage and also the subsequent period 

 of its gradual reduction. He shows that in very young specimens 

 the spinal cord reaches the extreme tip of the tail, and throughout 

 its length is quite uniform in structure. Somewhat later (embryos 

 11 to 15 mm. long) it can be divided at about the level of the thirty- 

 second vertebra into two parts; a cranial or main part, in an advanced 

 stage of development, and a caudal, slender part, retarded in develop- 

 ment. The main part, lying cranial to the thirty-second vertebra, 

 undergoes uninterrupted and progressive differentiation, whereas the 

 portion caudal to this undergoes regressive changes and, with the 

 exception of its extreme tip, finally becomes converted into a fibrous 

 strand, the tip forming the coccygeal medullary vestige. This, 

 therefore, is an instance in which a tissue undergoes reversion to an 

 earlier embryonic type, followed by a certain amount of subsequent 

 redifferentiation. Another instance of the same process was referred 

 to in the last report in connection with the growth of the cartilaginous 

 capsule of the ear. 



