(91 ) 



tlie anterior /one, in llic middle zone lliey exist, hnt continuity 

 between t!>e hinielhie of the Iieniispliercs and of the vcrnns remains, 

 and in tiie posterior zone they form a complete division between 

 the lamellae of the hemispheres and of the vernis. 



Anatomy. — 'UJn the sijniixithetic nervous si/deni in Mono tr ernes." 

 By A. J. P. V. u. Broek. (Communicated by Prof. L. Bolk). 



The following- description contains the results of an investigation 

 on the structure of the sympathetic nervous system in Monotremes. 



For this investigation I had at my disposal a female specimen of 

 Echidna aculeata and of Ornithorhynchus paradoxus. The sympathetic 

 system of the two specimens resemble each othei' in many respects, 

 i. e. in structure and ramitication ; in other respects they show 

 important difïerences from placental mammals. 



In the cervical sympathetic chord we find in Echidna one, in 

 Ornithorhynchus two ganglia. 



The ganglion cervicale of Echidna is (Fig. 1. g. c.) a rather large, 

 oval-shaped body, situated close above the Arteria subclavia. Singular 

 or double rami viscerates connect this ganglion with the first as far 

 as the fifth cervical nerves included. The ramus visceralis of the 

 first cervical nerve does not enter directly into the ganglion cervicale 

 but is joined to a nerve that appears at the upper end of this 

 ganglion and can be traced as far as the base of the skull (Fig. 1. a.) 

 where it enters into a little foramen. Close to the base of the skull 

 (Fig. 1. b.) two little twigs branch off this nerve, which go through 

 the M. longus colli to the vertebral column. Anastomotical branches 

 of this nerve with the Nervus vagus and the ramus descendens 

 hypoglossi are under the base of the skull. (Fig. 'J. c). 



In Ornithorhynchus a little part of the cervical ganglion, which 

 should be considered as the fusion of the ganglion cervicale supremum 

 and medium in placental mammals, is situated on the atlas as a ganglion 

 cervicale supremum (Fig. 2 g. c. s.) and is connected with the first 

 cervical nerve. A thick branch of the Nervus vagus enters into the 

 ganglion from the lateral side; at the medial side the Nervus laryn- 

 geus superior (Fig. 2 1. s.) leaves it. In its course this nerve contains 

 a little ganglion before dividing into ramus externus (Fig. 2 r. e. 1. s.) 

 and internu.s. 



The rami viscerales parting from the second to the fifth cervical 

 nerves included communicate in Ornithorhynchus with the ganglion 



7 



Proceedings Royal Acad. Amsterdam. Vol. VIll. 



