158 PHYSTOLOGY OF FARM ANIMALS [CH. 



blood during the ijroce.ss of erection. The corpus .spongiosum 

 is similar in structure but its fibrous framework is less well 

 developed. The wall of the m-ethral canal contains unstriated 

 muscle fibres. At its distal end the spongy body becomes enlarged, 

 forming the glans penis. At their proximal ends all the three 

 bodies are swollen into bidbous enlargements, those of the 

 cavernous bodies being surrounded by the ischio-cavernosus or 

 erector penis muscles, and that of the spongy body by the bulbo- 

 cavernosus muscle. The penis is supplied with blood by the pubic 

 arteries and the dorsal arteries, and the blood is carried away by 

 the dorsal veins and another set of veins communicating with the 

 prostatic plexus. The integument of the penis is a loose fold of 

 skin called the prepuce or foreskin which is especially thick in the 

 bull. Sebaceous glands emitting an odoriferous secretion par- 

 ticularly during rut are present near the free margin of the prepiace. 

 The peifis is very sensitive to extenial stimulation, its surface being 

 beset with numerous Paccinian corpuscles and other sensory end- 

 organs. 



The above description applies especially to the human penis, 

 but in the domestic animals the structure of the organ is essentially 

 similar. In the horse the end of the penis (the region of the glans) is 



II 



Fig. 79. Tenis of ram (from Marshall). 



rounded, and when inserted in a state of erection into the vagina of 

 the female occupies the greater part of that passage. In the ram 

 there is a peculiar filiform appendage attached to the left side of 

 the penis, the distal end of which appears to have undergone some 

 sort of torsion. The urethra opens to the exterior at the end of 

 the appendage. This structure, like the main portion of the penis, 

 is composed very largely of erectile tissue which surrounds the 

 urethra and may be regarded as an extension of the corpus 

 spongiosinn. Outside of the erectile tissue is a well marked 

 muscular layer which lies next to the integument. The appendage 

 is supported by a j^air of fibro-cartilage bodies placed one on 

 each side of the urethra throughout the whole length of the 



