LIFE AND WORKS OF NICOLAUS STENO XXI 



Only twice more in his subsequent writings Steno touched upon 

 the question of the brain. In his description of the dissection of a 

 shark he particularly emphasized the exceeding smallness of the brain, 

 expressing the supposition that many nervous fibres leading to the 

 muscles had their origin, not in the brain, but in the spinal cord. This 

 he maintained, partly because the sum of the transverse sections of 

 all nerves leading to the muscles was far larger than the transverse sec* 

 tion of the spinal cord at the bottom of the fourth ventricle, and partly 

 because the cervical and the lumbar enlargements were to be found 

 in vertebrates with four extremities, while no such formations were 

 to be found in vertebrates without extremities. In the same Treatise 

 Steno also touched upon other interesting questions concerning the 

 brain ; but it would take too long to dwell upon them here. 



In his last work upon the brain, treating of a hydrocephalic calf, 

 which he dissected in Innsbruck in 1669, Steno mentioned a number 

 of observations on the structure of the brain; he also discussed the 

 origin of the large quantity of fluid, and stated that he was of the 

 opinion that the four ventricles were, in reality, only one single cavity. 

 Finally he called attention to the fact that, though in this case the brain 

 was exceedingly disfigured, both sensation and motion were normal. 



In the description of his dissection of a ray Steno explicitly dwelt on TheRepro= 

 the peculiar eggsshells of this animal, which were in those days gene* ductiveOr= 

 rally looked upon as being the uterus of the animal. Steno pointed S* n lr a ^ ■. 

 out how this interpretation was in any case quite untenable; on the tion f t \^ e 

 whole he was not sure that these formations were really produced by Fetus. 

 rays; but if they owed their origin to these animals, they could not 

 be their uterus, but must be part of their eggs. 



At Steno's time natural philosophers were very uncertain as to how 

 the fetus was nourished in the uterus and in the egg. Some thought 

 that it received its food through the mouth, others that it received it 

 through the bloodvessels of the umbilical cord. Steno's explanation of 

 this process in placental animals was, as mentioned above, that the fetus 

 was nourished through the placenta by a secretion of the villi, which 

 he looked upon as glands. But once, when dissecting a newlyshatched 

 chicken, he found the vitelline duct and became aware of its conveying 

 the substance of the yolk direct into the intestine. As he had no idea 

 of the existence of such a formation, still less of its function, his sur* 

 prise was nearly overwhelming. He published this important discovery 

 as his own; but it appears from a passage in a later Treatise that he 

 was reproached with having done this, because, as his detractors main* 

 tained, the discovery had already been made by others. Concerning 

 the curious circumstances of this discovery, further particulars will 

 be found in the notes (vol. I p. 263 of the present Edition). 



In the description of his dissection of a shark Steno, after having 



