August 20, 1886.] 



SCIENCE. 



167 



cially of the thumb. Indeed, a proposition has been 

 made to us3 this characteristic for identifying the 

 Chinese emigrants to California. In Germany, espe- 

 cially, attempts have been made to show that these 

 markings have racial significance. Has it ever been 

 noticed that this custom has been borrowed from 

 China, where the thumb and finger markings are 

 used for purposes of identification, and by illiterates 

 in signing papers ? In the ' Proceedings of the China 

 branch of the Royal Asiatic society,' for 1847, p. 11, 

 is an article on land-tenure in China, by Thos. T. 

 Meadows. Appended to this article is a copy of a 

 deed bearing the thumb- signature of the grantor, a 

 woman. Chinese sailors shipping on junks are made 

 to sign with five fingers, in order to get a more cer- 

 tain identification. Dr. D. B. McCartee informs us 

 that the Chinese class the striae at the ends of the 

 fingers into ' pots ' when arranged in a coil, and 

 ' hooks ' when they form a curving loop. They say 

 that two men's thumbs may be alike, but that it is 

 hardly possible that their hands would make similar 

 pot-hooks. 



Walter Hough. 



U. S. national museum, Aug. 10. 



nerve-fibre courses in these small brains, a difficulty 

 which has been to a great extent removed by im- 

 proved microscopic methods ; second, from the fol- 

 lowing fact : the anterior commissure in the mam- 

 malian brain consists of two divisions, one going tO' 

 the olfactory lobes, the other to the temporal lobes. 

 Recent authors have been led to confuse the commis- 

 sure which really represents the corpus callosum^ 

 with the first-mentioned division of the anterior com- 

 missure, the truth being that the distribution of this 

 commissure has never been precisely observed. 



During the past w^inter I had an opportunity of 

 studying the cerebral commissures in types of all the 

 lower orders, in the most thorough manner ; and 

 found that the corpus callosum, so far from being a 

 structure peculiar to the mammals, is present in 

 the reptiles, birds, and Amphibia, and probably 

 also in the Dipnoi and other fishes. In short, this 

 commissure is a primitive character of the vertebrate 

 brain. An account of the steps which led to this 

 conclusion would exceed the due limits of this article, 

 but an outline of the results may be given. ^ 



For our present purpose, we must recall the em- 

 bryonic position of the mammalian corpus callosum 



Fig 1. — a vertical section of the frog's 

 brain {Rana esculenta) : acm, anterior 

 commissure ; cc, or cal, corpus cal- 

 losum; dc, ort)3, third ventricle ; fvi, 

 foramen of Monro ; It, lamina termi- 

 nalis ; pr, pineal gland ; Iv, lateral ven- 

 tricle; vc, ventriculus communis. 



The corpus callosum in the lower vertebrates. 



The corpus callosum, or great commissure of nerve 

 fibres connecting the cerebral hemispheres, has long 

 been one of the landmarks of comparative anatomy. 

 In every modern work upon zoology, this commissure 

 is given as a brain character which distinguishes the 

 mammals from the lower orders of vertebrates. In 

 fact, Owen long maintained that the corpus callosum 

 proper was wanting in the marsupials and the mon- 

 otremes ; and his authority on this point was gen- 

 erally accepted until Flower, in 1865, demonstrated 

 that this commissure is well developed in these ani- 

 mals, although much smaller in relation to the size of 

 the anterior commissure. These observations were 

 soon confirmed by Sander. 



It is an interesting fact, as an example of knowl- 

 edge apparently going backwards, that the earlier 

 anatomists, in studying these commissures, hit much 

 nearer the truth than their succe.'jsors. For instance, 

 that acute observer, Meckel, so long ago as 1816, cor- 

 rectly described the corpus callosum in the brain of 

 the duck, and Reissner found it in the brain of the 

 frog, in 1867. Other authors gave more or less ac- 

 curate accounts of this organ in the lower verte- 

 brates. More recently, in 1875, Stieda found it in 

 the brain of the turtle. In face of these statements, 

 all subsequent authorities, including Mihalkovics, Rl. 

 Riickhard, Bellonci, and Stieda (with the exception 

 of his one observation mentioned above), hold that 

 the corpus callosum first arises among the mammals. 

 This error, as it now appears, has sprung from two 

 causes : first, from the difficulty of following the 



as a delicate bundle, traversing the thin wall which 

 unites the hemispheres, and known as the ' lamina 

 terminalis.' Below this, in the lamina, is another 

 fibre-bundle, the anterior commissure. In the pla- 

 cental mammals, these bundles, from the time of their 

 first development, are separated by an interval or 



Fig. 2. — A vertical section 

 Europaea). 



of 



liph 

 the turtle's brain (Emyi 



septum ; but in the marsupial brain, at an early 

 stage, they lie close together in the middle line, very 

 much as they are represented in fig. 3, in the turtle's 

 brain {cal and acm), the upper bundle bending up- 

 wards, like a horseshoe ; the lower passing outwards 

 in the floor of the lateral ventricle (iv). 



In the brain of the frog, in vertical section (fig. 1), 

 we observe two bundles similarly placed in the lami- 

 na terminalis. The lowermost {acm) consists of two 

 parts of unequal size, the larger part passing for- 



1 See Morvhologisches jahrbuch, xii, August. 



