182 THE EXTERIOR OF THE HORSE. 



as well as maintained in its normal situation by a cutaneous fold, the 

 sheath, which we will examine first. 



1st. The Sheath. The sheath is to the penis what the scrotum 

 is to the testicles. 



Constituted by the skin, which, doubled upon itself from before to behind, 

 forms a kind of pouch open in front, it is destined to contain the free portion of 

 the penis in a state of non-erection. Between the layers of the integument which 

 forms the base exists a fibre-elastic expansion, called the suspensory ligament of 

 the sheath, a dependency of the abdominal tunic, to which it is attached on each 

 side. The skin in its interior is deprived of hair, irregularly folded upon itself, 

 soft, and unctuous from the numerous sebaceous glands, called the preputial 

 glands, which secrete a sebaceous material of a strong and disagreeable odor, 

 known by the vulgar and improper name of coom. 



The sheath is entirely effaced at the moment of erection of the 

 penis. Its development varies according to the animal : in the stallion 

 it is ample and generally little soiled by its secretion ; in the gelding 

 it is smaller, and its narrow opening sometimes prevents the protrusion 

 of the penis during micturition. There may result, in such a case, a& 

 Lecoq has remarked, hypersecretion by the sebaceous glands, irritation 

 from the urine, and even ulcerations difficult to heal, which may extend 

 to the penis. 1 



Warts, or papillomata, are in certain cases observed on the sheath. They 

 are regarded as contagious, although no irrefutable proof of this has as yet been 

 given. 



(Edema of the sheath depends upon a prolonged retention of the peni& 

 within it, upon the contact of the urine, or upon the presence of an excess of the 

 sebaceous secretion. It disappears readily under the influence of exercise and 

 cleanliness. 



Finally, melanotic tumors are met here, which by their volume sometimes 

 prevent the protrusion of the penis and interfere with the exit of the urine. 



There are some horses which produce during locomotion, particularly in the 

 trot and the gallop, a sound, always disagreeable, called the sound of the frog. It 

 ceases ordinarily at the end of a certain time during the exercise. Some persons 

 have incorrectly attributed it to the churning of the liquids and gases con- 

 fined in the caecum, a part of the large intestine remarkably developed in the horse, 

 We long ago made the remark that it is never heard in mares. Franconi, our 

 classmate and friend, informed us one day that it could be made to disappear by 

 packing the sheath with oakum. We have since verified the efficacy of this 

 ingenious means, the action of which is understood without difficulty, knowing 

 the mechanism by which this sound is produced. During locomotion the sheath 

 is alternately raised and lowered, and at the same time the penis executes in its 

 cavity more or less extensive to-and-fro movements. There results from this the 

 formation of a vacuum and the entrance of external air, which occasions thia 



1 F. Lecoq, Ext6rieur du cheval, p. 97. 



