A WEEKLY ILLUSTRATED JOURNAL OF SCIENCE. 



" To lite solid ground 

 Oj Nature trusts the mind which Suilds /oraye."—VfoKDS\\OKTH. 



THURSDAY, NOVEMBER 7, 1901 



T//E HIND-BRAIN OF THE MONOTREME. 

 Die Medulla Oblongata und die Vicrhiigclgegend von 

 Ornithorhynchus mid Echidna. Von A. Koelliker. 

 Pp. vi + 100. (Leipzig: Engelmann, 1901.) Price i6i'. 



DETAILED knowledge of the brain of the Mono- 

 treme has in recent years been considerably ex- 

 tended by the works of Profs. EUiot Smith, of Cairo, and 

 Ziehen, of Jena. Material suitable for successful prose- 

 cution of microscopical research in this field is necessarily 

 rare. It is a matter for congratulation that such material 

 should have reached the hands of a veteran histologist. 

 Prof. V. Kolliker. His monograph deals with the 

 arrangement of nerve-fibre bundles and of nerve-cell 

 groups in the mid-brain and hind-brain of ornitho- 

 rhynchus and of echidna respectively. The study is 

 based on transverse sections stained with ha^matoxylin 

 by the Weigert method for nerve-fibres. The ornitho- 

 rhynchus brain furnished for the regions studied a series 

 of 1088 sections. Detailed drawings under defined 

 enlargement are given for sections at eighteen of the 

 levels. Among the points of interest ascertained the 

 following appear the chief. 



Both monotremes offer in common certain features in 

 contradistinction to other mammalia. Noteworthy among 

 these are the subjoined. 



The fourth ventricle extends very far distally, so far, 

 in fact, that instead of the anterior half of the cell- 

 group of origin of the hypoglossal nerve, the whole 

 length of that cell-group lies practically uncovered in the 

 floor of the ventricle. The hypoglossal cell-group lies, 

 not ne.xt the raphe and under the longitudinal bundle, 

 but away at the side of the ventricle. 



The root of the cochlear nerve enters the bulb by 

 piercing it ventral to the peduncle of the cerebellum ; 

 none of its fibres wind round the peduncle. But the so- 

 called stria? acusticae exist nevertheless on the dorsal 

 aspect of the bulb. 



The facial nerve has, in addition to its regular nucleus, 

 a second widely separate and dorsal to that, near below 

 NO. 167 I, VOL. 65] 



the genu of the nerve root. The sensory root of the 



I trigeminus is very large, and enters the brain entirely 

 anterior to the pons. 



The pons is poor in cell-groups proper to itself. In 

 echidna there are some cell-groups in its lateral portions 

 as well as in the median, but in ornithorhynchus there 



I are no lateral cell-groups at all. 



I The great system of fibres — the " fillet " or sensory 

 system — ascending toward the brain and fed by 

 secondary relays from the usual recipient afferent cell- 

 groups is well developed, and exhibits the general arrange- 

 ment obtaining in higher mammals. On the other hand, 

 the system of fibres— the pyramidal — descending from the 

 hemispheres to form connections with the efferent nuclei 

 is so poorly developed that its very existence is not 

 absolutely certain, at least for ornithorhynchus. It is of 

 interest to note that the great efferent cerebral system 

 can coexist in so meagre an extent in forms which 



j possess an afferent spino-cerebral system so extensive. 



I Thus as a permanent condition we have a state of things 



I similar to that which regularly forms a transient stage 

 in the development of the higher type of mammalian 

 nervous system. 



! Among features of interest offered by the two brains 

 individually, and therefore to be considered more or less 

 apart each from the other, are the following : 



In ornithorhynchus, with its small cochlear nerve, there 

 is discoverable only a mere trace of any superior olive. 



I In echidna, with its large cochlear nerve, the superior 

 olive is a structure of considerable extent. 



In echidna a large system of fibres passes along the 



i lateral region of the bulb to the outer side of the sensory 

 root of the trigeminus. These fibres in the upper pontine 

 levels bend inward, decussate, and ascend again in the 

 pes pediinciiU cerebri of the crossed side. They are 

 traceable at least as far as the optic thalamus. Kolliker 

 urges that it is a sensory spino-cerebral system, but the 

 merely anatomical method employed affords no trust- 

 worthy guide to the functional direction of the path. 



The central nervous system of echidna represents, on 

 the whole, a grade of development distinctly superior to 

 that of ornithorhynchus. Traces of a pyramidal system 

 fairly distinct though very scanty can in echidna be 



B 



