290 University Geological Survey of Kansas. 



fishes (Mugil, etc.) Between the anterior and posterior processes 

 the basal pieces are excavated to receive the bases of the neural 

 arch, as shown in the figure. The two basal pieces of each 

 vertebra are distinct. Together they seem to form a saddle in 

 which the neural arch rides. 



I find this same structure of the neural arches in some of 

 the vertebrae belonging to specimens in the United States Na- 

 tional Museum ; but in one section of connected vertebrae an 

 arch like those above is succeeded in the next vertebra by an 

 arch in^which every trace of a suture between the arch and the 

 apparent basal piece is lost. This vertebra is shown in fig. 2. 

 The form of the base of the arch is not greatly different from 

 that of the arch with accessory piece in fig. II, 55 and we may 

 even convince ourselves that we can trace a part of the bound- 

 ary line between the two portions. There is evidently at this 

 point of the vertebral column a sudden change from neural 

 arches furnished with basal accessory pieces to arches without 

 these, or consolidated with them. Further backward the form 

 of the arches becomes modified somewhat, so that they resemble 

 the one shown in fig. 3. A section fourteen inches long and 

 containing seven vertebrae having arches of this kind is before 

 me. This condition shows us that the neural arches which are 

 provided with basal pieces are confined to the anterior or middle 

 portion of the tail region, while the hinder portion contains no 

 such vertebral structures. We are reminded that in Amia the 

 middle portion of the caudal vertebral column is composed of 

 two for each muscular segment, while the anterior and poste- 

 rior portions have the vertebral centra of the ordinary kind. 

 It seems as if the tail portion of the vertebral column of the 

 amioid fishes and of the Isospondyli retained primitive condi- 

 tions longer than the abdominal portion. 



It is difficult to determine what explanation is to be given of 

 the presence of these basal pieces. The so-called zygapophyses 

 of fishes are regarded as being outgrowths of the neural arches 

 — exogenous and not autogenous processes. It might be said, 



55. Fig. 11, in Professor Hay's article, refers to the pelvic actinosts, and seems to have no 

 connection with the subject. 



