502 ANATOMICAL TECHNOLOG F. 



(8) Continuity of the rhinalis with the postrhinalis ; of the Sylman with the point of 

 their junction ; of the superorbital with the rhinalis ; of the callosal with the hypocampal, 

 and with the prceradicalis when present. 



1367. Variable Characters. (1) More or less frequent presence of the following ten 

 inconstant fissures : confinis, falcialis, intermedia, lunata, medUateralis, postcruciata, post- 

 margin<ilis, postradicalis, prceradicalis, subfalcialis. 



(2) Frequent union of the ansata with the coronalis and lateralis ; of the lateralis with 

 the ansata and medilaleralis ; of the diagonalis with the anterior; of the supersykian 

 and postica ; of the marginalia with the postmarginalis. 



(3) Occasional unions of the medilateralis and confinis ; of the crutiata and the sple- 

 nialis. 



(4) Very rare unions of the postica and the rhinalis ; of the anterior with the super- 

 syltian. 



1368. Homology of the Human and Feline Fissures. The determination of the 

 identity of the human fissures with those of the other Mammalia has long been desired from 

 the standpoint of Comparative Morphology and Systematic Zoology. Referring in 1868 to 

 his Lectures on the Brain in 1842, Owen says (A, III, 116) : " The main object which I 

 had in view was the determination of the homologous and superadded convolutions in the 

 more complex prosencephalon of man." 



Since the discovery in 1870 by Fritsch and Hitzig (1) of the electrical excitability of 

 certain areas of the cerebral cortex in the dog and cat, and the confirmation of this upon 

 monkeys by Ferrier (A, 138), there have been likewise physiological and psychological 

 reasons for the determination of these fissural homologies, and at this time probably few 

 biological events would be more generally welcomed than the presentation of incontro- 

 vertible evidence as to the human homologue of the carnivoral Fissura cruciata, or the 

 representative of the human centralis (Fissure of Rolando) in the cat and dog. 



1369. The following are sufficient general examples of the difficulties which sur- 

 round the subject and of the differences of opinion among high authorities : 



Gratiolet wrote (A, 10) : 



" We need only compare the brain of an ape with that of a carnivore or a ruminant to 

 see that the convolutions present very dissimilar general arrangements in the several 

 orders of Mammalia. These differences are so great that it would be imprudent to estab- 

 lish corresponding subdivisions and to investigate their homologies. In fact, this ques- 

 tion has as yet no basis of certainty, and we think that for the present it should not be 

 undertaken." 



Owen says (iJo) that the same names apply to the fissures of the Aye-aye and the cat, 

 while the very next paper in the volume of the Zoological Transactions contains the 

 admission of Flower (6) that, as between the Lemurs and the Carnivora, the " nomencla- 

 ture utterly fails." 



1370. Special examples of the diversity of opinion are furnished by the two fissures 

 already named, the cruciata or " frontal " of the cat and dog and the centralis of man. 



The centralis is homologized with the superorbitalis bv Duval and Keller (A, 57, note), 

 and apparently by Broca ; Hitzig (A, 136, 137, Fig. 10, 11) makes it equivalent to the 

 ansata together with a part of the supersylviana, a view which derives some support from 

 the occasional interruption of the human centralis ; it is the homologue of the coronalis 

 in the opinion of Owen (A, III, 130), Meynert (1), and Pansch (1, 47). In an earlier 

 paper, however, Pansch regarded the centralia as homologous with the cruciata, and 

 this is the opinion of Ferrier and Clevenger. 



The cruciate fissure of the Carnivora is said by Ferrier (A, 199) to be experimentally 

 the equivalent of the centralis, and Clevenger (2, 14) states that the two fissures are " his- 



