254 THE PHYSIOLOGY OF REPRODUCTION 



At their proximal ends the three corpora are enlarged into bulbs. 

 Those of the cavernous bodies are covered by the ischio-cavernosi 

 muscles (or erectores penis), while the bulb of the spongy body is 

 surrounded by the bulbo-cavernosus muscle (or ejaculator urinse). At 

 its distal end the- corpus spongiosum becomes enlarged, forming the 

 glans penis, which is identical in structure with the rest of the body. 



The integument of the penis in the region of the glans becomes 

 doubled in a loose fold. This is the prepuce or foreskin. Numerous 

 sebaceous glands are present near the free margin of the prepuce. 

 These glands emit an odoriferous secretion which in some animals is 

 especially marked during the season of rut. 1 



The penis is very sensitive to external stimulation, its surface 

 being beset with simple and compound end-bulbs and Pacinian 

 corpuscles, especially in the region of the glans. 



The various kinds of end-organs in the external genital organs of 

 both sexes have been described at some length by Luciani, 2 to whose 

 work the reader is referred. There are genital corpuscles, the nerve 

 fibres to which divide into five branches which end in knobs (Krause's 

 end-bulbs), as well as typical Meissner's corpuscles which are 

 capsulated and usually oval or elongated in shape, with a complex 

 and variable structure, and a series of transitional forms passing t 

 imperceptibly from Pacinian corpuscles to more elaborate structures. 

 The end-organs in the glans penis are not uniformly distributed, and 

 Head, 3 taking advantage of this fact, was able to carry out an 

 interesting experiment illustrating sensory dissociation and the 

 inhibition of afferent impulses by other antagonistic impulses which 

 become dominant. It was found that the tip of the glans may be 

 devoid of heat-spots or end-organs responding to the sensation of heat, 

 but in possession of others which are sensitive to cold and pain. In 

 such a case " the end of the penis was dipped into a glass containing 

 water at 40 C. ; since no heat-spots were present and this temperature 

 has no effect upon the cold-spots, the only sensation evoked was a 

 peculiarly disagreeable pain. When, however, the temperature of 

 the water was raised to 45 C., pain was to a great extent displaced 

 by a vivid sensation of cold, due to stimulation of the cold-spots. 

 Instead of increasing the discomfort an elevation of temperature 

 ceased to be strictly painful because of the appearance of the specific 

 sensation of ' paradox cold.' But around the corona the penis is 

 always well furnished with heat-spots in addition to those for cold 



1 Courant, " Uber die Praputialdriisen des Kaninchens und iiber Verander- 

 ungen derselben in der Brunstzeit," Arch. f. Mikr. Anat., vol. Ixii., 1903. 



2 Luciani, Human Physiology, English Translation, edited by Holmes, vol. iv., 

 London, 1917. 



3 Head, " Release of Function in the Nervous System," Croonian Lecture, 

 Proc. Roy. Soc., B., vol. xcii., 1921. See also Head, with Rivers, Holmes, 

 Sherren, Thompson, and Riddoch, Studies in Neurology, London, 1920. 



