MORPHOLOGY OF THE CEREBRAL CONVOLUTIONS. 305 



man, PI. XLI, fig. 3. I have not met with it, nor, so far as I am aware, has this 

 connection been found in the brains of any of the Simiada^. 



Pansch, Ecker and most other writers consider this fissure as a primary and 

 fundamental furrow. It is true that in the brain of Man and the higher Simians 

 this fissure is constantly present, and that it forms a sure point of departure in 

 searching out the convolutions in Man is also a fact, but this alone is not a sufficient 

 reason for considering it as a primary and fundamental typical furrow of the Pri- 

 mate brain. Other fissures than this are far more constant, such for instance as the 

 superior occipito-temporal, o.t. 1 , which is the most persistent of all the fissures of 

 the lateral surface of the hemisphere except the Sylvian, being found as a well 

 marked furrow in all the Primates, with the exception of some of the Marmosets, 

 such as Hapale midas, etc. The central is absent in many of the lower forms, 

 such as the Lemuridae and it is only as we approach the higher Simiadse that it 

 gradually assumes a high state of development, reaching its most fully developed 

 condition in Man. In Ckrysothrix, PL XXXVIII, fig. 9, the superior occi- 

 pito-temporal is well developed, but the central is barely perceptible as a slight in- 

 dentation, c c. Certainly, therefore, on the grounds of constancy, it must be con- 

 sidered simply as a peculiar development of one of the constant fissures of the 

 lateral surface, of the same morphological value as the occipito-temporal and frontal 

 fissures, and is by no means to be placed in the same category with such fissures as 

 the Sylvian, the fissura tri-radiatus of the mesial surface, or even with the fissures 

 forming the primary occipital arch, fissura occipitalis superior et inferior. 



Occasionally it is bridged over and its continuous course interrupted by annec- 

 tant gyri. I have never observed this myself, but it may be seen in the figure of 

 the brain of the great clinician, Dr. Fuchs, figured by Wagner. It appears in the 

 human foetus in the beginning of the sixth month, as may be seen in Plate XXXV, 

 fig. 7, c c, the frontals, temporals and interparietals making their appearance at 

 about the same time, Plate XXXV, fig. 8. The central fissure appears to me to 

 have morphologically the same value and significance as these fissures. In fact it 

 may be considered as comparable to the posterior portion of a superior occipito- 

 frontal fissure, which, owing to the mechanical condition produced by the excessive 

 development and growth of the occipito-frontal lobe as compared with the occipito- 

 temporal, develops downward, separating from its anterior portion, and carrying 

 with it its accompanying convolutions, A. C. and P. C, fig. 1, Plate XLII, the 

 so-called anterior and posterior central convolutions, which are, therefore, to be 

 regarded morphologically as displaced posterior portions of the superior and middle 

 frontal convolutions. The central fissure, owing to this downward development, 

 becomes completely separated from the superior frontal fissure. Owen 1 has also 

 reached the same conclusion. 



In the Lemurs, Plate XXXIV, figs. 16 and 17, no sign of a distinct and sepa- 

 rate fissure is present; and a series of these brains will give a perfect illustration 



1 Comparative Anatomy of Vertebrates, Vol. III. 



