FUNCTIONS OF THE MAMMARY GLANDS. 291 



layer of cellular tissue containing a large number of elastic 

 fibers and smooth muscular fibers which depart slightly from 

 the axial line in direction, though insufficiently so to be termed 

 "spiral" as in the case of the sweat-gland muscles. But, in 

 the mammary gland, suckling, by creating a vacuum and caus- 

 ing elongation of the nipple, fulfills the function of the latter. 



"We thus have all the structural elements of the previously 

 studied glands present in these. Their peripheral mechanisms 

 should also correspond, however. As to the nervous supply, 

 we have seen that dilation of arteries was found to be con- 

 trolled by motor nerves, by Laffont, and that the presence of 

 vasomotors was denied by de Sinety. Hence, the vasodilation 

 must be due to indirect action, especially since Laffont caused 

 it by stimulating these nerves, precisely as Claude Bernard had 

 done in the case of the submaxillary glands. The stimulation 

 must, therefore, have caused this indirect vascular dilation 

 in the manner described when the chorda tympani was in 

 question: i.e., by causing constriction of some of the glandular 

 vessels. That this conception of the process is justified is 

 further sustained by the experiments of Rohrig, 17 who found 

 that a motor nerve, the external spermatic, supplied constrictor 

 fibers to the glandular blood-vessels in the goat, and that 

 division of one branch of this nerve, the lower, enhanced secre- 

 tion (evidently due to relaxation of the vessels through loss 

 of their normal stimulus), while stimulation of the peripheral 

 end of this subdivision of the nerve decreased the secretion. 

 This clearly suggests that, just as is the case in the submax- 

 illary gland, each motor nerve of the mammary gland gives off 

 two subdivisions: one evidently to the vascular walls, the other, 

 as we have seen, to the glandular elements. 



As to the sympathetic fibers, they are also stated by Eoger 

 Williams to "accompany the mammary blood-vessels"; and, as 

 section of a sympathetic nerve is always followed by dilation 

 of the arteries, they can only act as vasoconstrictors here as 

 elsewhere. That all efferent fibers distributed to the gland- 

 ular elements and to the blood-vessels originate from the 

 general motor system is evident when their relationship with 



Rohrig: Virchow's Archiv, vol. Ixvii, 1876. 



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