78 ORIGINAL ARTICLES. 



The brothers Wenzel figure in their excellent plates the various con- 

 ditions of the posterior cornu and hippocampus minor to which they refer; 

 and it is remarkable that the brain which they have selected as exem- 

 plifying the absence of the hippocampus minor on both sides, Tab. v., 

 Fig. 1, is said to be "ex triginta annorum sethiope," while the most re~ 

 markably developed hippocampus, Tab. vii., Pig. 3, is "ex septem 

 annorum puero." 



The work whence these extracts are taken is contained in the libraries 

 both of the College of Surgeons and of the Eoyal Society; but, even if it 

 were inaccessible, a well-known and more modern writer fully bears out 

 the doctrine it contains. I refer to Longet,** who states that, in the 

 human brain, w the posterior cornu is found of very different lengths and 

 breadths. I have found brains in which it extended up to within a few 

 millimetres of the surface of the posterior lobe, and others in which it 

 ended at more than three centimetres therefrom." 



The same excellent authority, in describing the posterior cornu of the 

 lateral ventricle, says :— 



"Its inner and lower wall is raised by a convolution which forms a more or less 

 distinct, and at times, double projection into the cavity itself. This projection (Hippo- 

 campus minor, eminentia unciformis, calliculus, unguis, calcar avis) was well described 

 by Morand, and after him was called the ' Spur of Morand' — 'Ergot de Morand.' 



" The Hippocampus minor exhibits differences in its form and circumference, as 

 Greding has stated ; usually it is bent on itself, arched forwards and outwards, some- 

 times narrow and long, sometimes broader. Very frequently it is smooth, at other times 

 it exhibits many fissures and small enlargements, especially posteriorly ; or it may be 

 divided by a longitudinal cleft into two halves, the upper of which is almost always 

 larger than the lower. Its dimensions are by no means directly proportional to the de- 

 velopment of the posterior lobe. In the same subject it may be very distinct upon the 

 one side, and yet be hardly perceptible upon the other. For the rest I can certify that, in 

 spite of Meckel'sf assertion to the contrary, it is not always present. My own observations 

 agree with those of Wenzel, who, among fifty-one subjects that he examined with express 

 reference to this point, found three in which the hippocampus was absent upon both 

 sides, and two in which every trace of it was absent upon one side only." 



To allow a structural character totally absent in six per cent, of the 

 members of any group to stand as part of the definition of that group, 

 considered as a sub-class, would be a very hazardous proceeding. But, 

 is it true that the hippocampus minor is altogether absent in the highest 

 apes ? I suspect that Tiedemann is responsible for the not unfrequently 

 admitted doctrine that it is; for, in the " Icones" he writes : — 



" Pedes hippocampi minores vel ungues, vel calcaria avis, quae a posteriore corporis 

 callosi margine tanquam processus duo medullares proficiscuntur, inque fundo cornu pos- 

 terioris plicas graciles et retroflexas formant, in cerebro simiarumdesunt ; nee in cerebro 

 aliorum a me examinatorum mammalium occurrunt. Romini ergo proprii sunt." 



* German edition, by Hein, under the title, Anatomie und Physiologie des Nerven- 

 systems des Menschen und der Wirbelthiere, 1847, Bd. i., p. 463. 



f Dr. Hein here adds: "What Meckel says is that he himself never failed to find the 

 hippocampus minor, but that he by no means wishes to throw doubts on Wenzel's state- 

 ments ;" and on reference to Meckel's work, I find this to be quite correct. 



