114 Journal of Comparative Neurology and Psychology. 



ScHENK and Birdsell published, in 1879, '^he results of their ob- 

 servations on certain mammalia, which, as Balfour says, "seem to 

 indicate that the main parts of the sympathetic system arise in conti- 

 nuity with the posterior spinal ganglia; they also show that in the neck 

 and other parts the sympathetic cords arise as a continuous ganglionic 

 chain."' Onodi ('86), working on elasmobranchs, agrees essen- 

 tially with Balfour, and gives excellently clear figures intended to 

 show that the cells which form the sympathetic cord arise as outgrowths 

 from the spinal ganglia. 



Paterson, in 1891, revived the idea of the mesoblastic origin of 

 the sympathetic nervous system. According to his researches on 

 mouse, rat, and human embryos, the earliest traces of the sympathetic 

 are seen as a cellular cord lying in the mesoblast between the aorta and 

 the cardinal vein, in the anterior dorsal region. This cord is bilater- 

 ally symmetrical, and is composed of cells which he claims are differ- 

 entiated mesoblastic cells. At the time of its appearance, the cord has 

 no connection whatever with the spinal nerves nor ganglia, and con- 

 stitutes the anlage of the sympathetic. The next step is the formation 

 of the rami communicantes, which arise as fibrous outgrowths passing 

 from the spinal .nerves to the sympathetic cord. The ganglia appear 

 next, and are formed at the points where the rami join the cord, result- 

 ing presumably from the growth of both sympathetic cells and nerve fi- 

 bers. The collateral sympathetic is developed by the outgrowth from 

 the sympathetic cord of cellular branches, which later give rise to the 

 ganglia, nerves, and plexuses. In this category are placed the cervi- 

 cal and sacral portions of the sympathetic chain and also rather doubt- 

 fully, the grey rami communicantes. This view is repeated by Pat- 

 erson, in 1903, in Cunningham's Anatomy. 



Marshall ('93), on the other hand, agrees very closely with the 

 theory advanced by Balfour. In frog and chick embryos, Marshall 

 finds that the sympatetic nervous system arises "as a series of out- 

 growths from certain of the cranial and from all of the spinal nerves. 

 These develop ganglionic swellings,""' which later become connected by 

 fibrous commissures, thus forming the gangliated chain of the adult. 



His, Jr. ('97), tracing in the chick the history of an anlage similar to 

 that described by Paterson, finds, in very early stages, that the cells 

 forming it come from the ganglia of the spinal nerves, thus confirming 



'^^^ Comparative Embryology.'''' Vol. 2, p. ^84. 

 In yertebrate Embryology.'''' Page IJ4. 



