24 INTRODUCTION TO SEXUAL PHYSIOLOGY 



It has been suggested that the secretions of the accessory 

 male organs may exert some beneficial influence on the female 

 organism, and there is some evidence that they are absorbed in 

 a quantity sufficient to produce definite effects, but whether 

 (his occurs is still doubtful. 



The penis is the intromittent organ of copulation. In addition 

 to conducting the urine to the exterior through the urethral 

 channel, it serves to convey the semen (including the secretions 

 of all the accessory glands above mentioned) into the genital 

 passages of the female. This latter function is rendered possible 

 by the power of erection, whereby the penis can be inserted into 

 the vagina in the act of copulation. 



The erectile tissue of the penis is mostly contained in three 

 tracts, the two corpora cavernosa which are placed one on each 

 side and are united in the middle line, and the corpus spongiosum 

 which is situated internally and surrounds the urethra. The 

 corpora cavernosa are enclosed by an integument containing 

 fibrous and elastic connective tissue and unstriated muscle fibres, 

 and giving off trabeculse which divide the structures into blood 

 sinuses or spaces. The corpus spongiosum is similar, but its 

 fibrous framework is not so well developed. Prior to copulation 

 the sinuses become engorged with blood, the outward flow of 

 which is arrested by the contraction of certain muscles (the 

 ischio-cavernosus or erector penis and the bulbo-cavernosus) 

 at the base of the penis where they surround the bulbous enlarge- 

 ments of the three corpora. The glans penis at the distal end 

 of the organ is formed by the enlargement of the corpus 

 spongiosum. 



The penis is supplied with blood by the pubic and dorsal 

 arteries, and the veins which convey the blood away are the 

 dorsal veins and another set communicating with the prostatic 

 plexus. 



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

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

 is removed in circumcision. A number of sebaceous glands are 

 present near the free margin of the prepuce, and these in some 

 mammals emit an odoriferous secretion during rut. The penis 

 is especially sensitive to external stimulation, its surface being 

 beset with sensory end organs of various kinds, particularly in 

 the neighbourhood of the glans. 



