PECULIARITIES OF CIRCULATION IN DIFFERENT PARTS. 359 



tion may be produced, and in the case of the penis, emixxio wnirm'* mav 

 bo effected, by local irritation. The erectile tissue appears essentially to 

 consist of a plexus of veins with varicose enlargements, inclosed in a fibro- 

 muscular envelope with trabecular partitions. 1 In the penis, as first pointed 

 out by Prof. Miilleiy there are two sets of arteries ; those of one set, des- 

 tined for the nutrition of the tissues, communicating with the veins in the 

 usual way, through a capillary network; whilst the others, termed by him 

 the "helicine arteries," are short, tendril-like branches which project into 

 the veins (covered, however, by their endothelium), sometimes singly, and 

 sometimes in tufts, ending abruptly by dilated extremities. These arteries 

 are accompanied by a special system of longitudinal bundles of muscles, 

 the fibres of which become inserted into the middle coat at various points 

 (Stilling, Stein). The dilated ends of the helicine arteries usually com- 

 municate directly with the venous cavities, since injection thrown into the 

 former generally fills the latter, and Kolliker states that he has frequently 

 found them giving off delicate, almost capillary vessels, which discharge 

 themselves into the venous spaces. The nerves implicated in producing 

 erection in the dog were found by Eckhard 3 to be, first, the Nn. pudend. 

 communes proceeding from the sciatic plexus, and supplying the musculi 

 ischio-cavernosi, the corpora cavernosa of the penis, and membranous por- 

 tion of the urethra ; and second, the Nervi erigentes proceeding from the 

 sacral nerves and entering the hypogastric plexus. This plexus contains 

 minute ganglia, communicates with the posterior meseuteric plexus, and 

 furnishes branches to the bladder, prostate gland, rectum, and membranous 

 portions of the urethra. After division of the former, or common pudendal 

 nerves in the dog, Eckhard found it impossible to produce erection of the 

 penis or emission of semen by direct irritation of the penis. The Nervi 

 erigentes are, undoubtedly, the chief excitors to erection, for on exposing 

 and irritating them, swelling of the penis, gradually proceeding forwards to 

 the glans, immediately commenced. Erection may also occur as a result of 

 certain emotional conditions of the mind, the influence of which is prob- 

 ably transmitted through the Sympathetic nerve, as it may be experienced 

 even in cases of paraplegia, whilst according to Legros, 4 after section of the 

 sympathetic fibres distributed to an erectile organ no erection occurs. The 

 precise mode in which the nerves act is still unknown, 5 but there are grounds 

 for believing that both the male and female organs are preserved in a qui- 

 escent state by a tonic influence exerted over the vessels by centres situated 

 in the lower part of the spinal cord. In the venereal orgasm, however, in- 

 hibitory centres are excited, which restrain the action of the spinal cord 

 and lead to dilatation of the vessels, and increased flow of blood through 

 the organ ; Eckhard, indeed, relates that in his experiments he obtained 



1 See A. W. Stein, New York Med. Journal, June, 1872, for an account of the 

 Histology and Physiology of the Penis. 



2 Entdeckung der bei der Erection wirksamen Arterien, in Miiller's Archiv, 1835, 

 p. 2''2. The views of Miiller, though opposed by Viilentin (Miiller's Archiv, 1838, 

 p. 182), Weber, Arnold, Beclard, and others, as well as recently by Ruget, Journal 

 de 1'Anatomie, t. i, p. 326, and Lander, Wien. Sitz., xlvi, 1803, p. 120, who consider 

 the helicine arteries to be for the most part, if not altogether, artificial products con- 

 sequent on the difficulty of forcing injection into the tortuous vessels of the tra- 

 beculae, have been supported by the great authority of Henle (Handbuch d. Mensch. 

 Anatom., 1866, p 402). See also Robin, pamphlet, On the Erectile Tissues, and 

 Vulpian, Legons sur 1'Appareil Vasomoteur, 1875, p 1G1. 



3 Beitrage zur Anat. und Phys., Giessen, 1863, and 1867, p. 71. 



Gaz. Med de Paris, 1866, No. 6. 



5 For different views see Kolliker, loc. cit. ; Rouget, Archives de Physiologic., 

 18(18, p. 671 ; Goltz, Pfluger's Archiv, 13. vii, 1873, p. 346; Vulpian, 

 1'Appareil Yasomoteur, 1875, p. 161 et seq. 



