PRIMORDIAL CRANIUM OF THE CAT 373 



tions suggest the possibility of the dorsum sellae of different spe- 

 cies not being strictly homologous. Gaupp says ('00, p. 538) 

 "Dass die hinten begrenzende Crista sellaris, wie sie bei dem 

 Chondrocranium der Saurier (und auch bei dem der Vogel) 

 vorkonunt, der Sattelsehne des Saugercranium entspricht, ist 

 allgemein anerkannt." But does the crista sellaris of reptiles 

 compare with the dorsum sellae of mammals? And are the latter 

 strictly homologous in the different orders of mammals? 



This is not the time for a full discussion of these questions 

 which requires a larger basis of observations, but a few comments 

 may be offered. Regarding the homology of the dorsum sellae 

 among the mammals the following may be noted. The saddle- 

 back of the chondrocranimn. of Echidna (Gaupp '08), Talpa (Noor- 

 denbos, '05), Caluromys and Didelphis (my own observation) is 

 very low. As already stated, Fischer denies its presence alto- 

 gether in the Talpa embryo he studied. In contrast wdth the 

 insignificant low ridge-like dorsum ephippii of these species is 

 the high saddle-back of the chondrocrania of man, apes, rabbit 

 and cat. In all these species evidence is at hand indicating the 

 presence of an element in the dorsal part of the saddle-back, more 

 or less independent of the base of that structure. In embryos 

 of cat smaller than the stage modeled, the notochord terminates 

 in a mass of mesenchjana which surmounts the crista transversa, 

 whereas in the latter stage it ends in the perichondrium of a car- 

 tilaginous tubercle which rises from the middle of the transverse 

 crest. This tubercle is developed from the mesenchymal mass, 

 and may possibly have its beginning in the prochondral nucleus 

 observed in the embryos of earUer stages (p. 327). In the cat 

 embryo of the stage modeled, the dorsmn sellae is formed to 

 some extent also from the up-turned edge of the parachordal 

 plate (crista transversa). It would seem, in respect to the con- 

 trast between the caudal hmits of the hypophyseal fossa in the 

 two groups here presented, that there is an element present in 

 the one which is not found in the other, or that in one group a 

 simple crista transversa forms the back of the pituitary fossa, 

 whereas in the other a crista transversa plus an additional ele- 

 ment enters into the construction of a dorsum sellae. 



