284 Susanna Phelps Gage 



above is seen to rise between the hemicerebrums (Fig. 95, 

 96), and is the ridge over which the endyma is reflected to 

 form the partition between the hemicerebrums, this partition 

 being in reality a plexus in the aula — auliplexus. Caudad of 

 the reflection of the auliplexus it projects as a ridge into the 

 aula, gradually becoming lower, and contains fibers probably 

 of connective tissue, which are directed toward a mesal blood 

 vessel (Fig 96), extending into it as in diemyctylus. Rabl- 

 Riickhard shows a ridge in this situation in a bony fish (40). 

 No such structure was detected in the lamprey. 



The discussion of this apparently insignificant part of the 

 brain has been introduced under the name crista, since that 

 term has been used by Wilder (53) to designate a small, 

 rounded body, seen from the aula resting upon the fornix and 

 dorsad of the precommissure, in the adult cat and sheep and 

 human embryos. At his suggestion, sections of this region 

 in the cat have been made. Figures 48, 49, are through 

 the columns of the fornix. The only noticeable fea- 

 ture in the structure is the fact that it contains rows 

 of cells which are arranged at right angles to those of the 

 fornix and that pia is found between the columns of the 

 fornix extending almost to the crista. If, as in the fornix 

 and other situations, these rows of cells indicate arrangement 

 of fibers, it is not improbable that fibers may be present here 

 which represent those seen in diemyctylus. The pia is cut 

 off" from actual entrance into the crista by the close union of 

 the fornicolumns, but the appearance is very suggestive of 

 that in diemyctylus, though there is no complete likeness of 

 ' structure. In position it seems comparable to that body in 

 diemyctylus, as it lies in the primitive terma which is dis- 

 guised by the growth of the callosum and fornix, between the 

 portae, near the point where the auliplexus is reflected, and 

 in the same morphological relation to the precommissure ; 

 hence the term crista is used to designate the part in diemyc- 

 tylus and amia, and if found in other forms will be a valuable 

 landmark in determining the relations of aula and commissures. 



