336 CIRCULATION. 



Robin has lately noted a peculiarity in the small vessels 

 of the brain, spinal cord, and pi a mater, which is curious, but 

 the physiological function of which is not yet apparent. 1 

 These vessels are surrounded by a thin, amorphous sheath, 

 which has a diameter of from - A ^ to -^^ of an inch greater 

 than that of the vessel itself. Between this and the blood- 

 vessel is a transparent liquid. This structure, which has 

 been observed in no other part of the circulatory system, is 

 regarded by its discoverer as the commencement of the lym- 

 phatics of the nervous centres. What effect this disposition 

 of the vessels may have upon the facility with which they 

 may become dilated or contracted, it is difficult to determine. 



Circulation in Erectile Tissues. In the organs of gener- 

 ation in both sexes there exists a tissue which is subject to 

 great increase in volume and rigidity, when in a state of what 

 is called erection. The parts in which the erectile tissue ex- 

 ists are, in the male, the corpora cavernosa of the penis, the 

 corpora spongiosa, with the glans penis ; and in the female, 

 the corpora cavernosa of the clitoris, the gland of the clitoris, 

 and the bulb of the vestibule. In addition, Rouget has lately 

 demonstrated the presence of true erectile tissue in the body 

 of the uterus, and in a bulb annexed to the ovary of the hu- 

 man female, but states that it is not found in the inferior 

 animals. He has shown by injections that the uterus is 

 capable of erection like the penis. 2 In some other parts, 

 such as the nipple and the mucous membrane of the 

 vagina, which are sometimes described as erectile, the pecu- 

 liar vascular arrangement which is characteristic of true 

 erectile tissues is not found. In the nipple, the hardness 

 which follows gentle stimulation is simply the result of con- 

 traction of the smooth muscular fibres with which this part 



1 ROBIN, Sur une Tunique Appartenante en propre aux Capillaires Encephalo- 

 Hachidiens. Journal de la Physiologic, etc,, Oct. 1859, tome ii., p. 643. 



2 ROUGET, Recherchcs sur les Organes Erectiles de la Femme, etc. Journal 

 de la Physiologic, Paris, 1858, tome i., pp. 320, 479, 735. 



