360 THE ANATOMY OF THE HORSE. 



an external longitudinal, and an inner circular set. To compensate for 

 the expansion of the uterine wall during pregnancy, and to provide a 

 force to expel the foetus at parturition, there is, during pregnancy, both 

 an increase in the size, and an addition to the number, of these 

 muscular fibres. 



3. The Mucous Coat forms a complete lining to the uterus. It is 

 smooth, of a pale pink colour, and thrown into longitudinal wrinkles. 

 The epithelium is simple, columnar, and ciliated, except in the posterior 

 part of the cervix, where it is stratified and squamous, as in the vagina. 

 In the cornua and body the mucous membrane is set with numerous 

 utricular glands. The mouths of these glands open on the surface of 

 the membrane, while their blind ends lie against the muscular coat. 

 They lie obliquely in the membrane, and are branched at their deep 

 ends. They are lined by a single layer of columnar ciliated cells. 



The mucous membrane of the cervix contains numerous mucous 

 follicles, and the peculiar ovula Nabothi, which appear to be mucous 

 glands distended into a vesicular form by their own clear secretion. In 

 pregnancy these cervical glands secrete the mucous plug that closes the 

 OS uteri. 



Directions. — The student must now return to the dissection of parts 

 remaining in the pelvis, beginning with the lumbo-sacral plexus (page 

 349). 



THE TAIL (fig. 48). 



Directions. — Saw through the ilium that is still intact, making the 

 section across the bone at the great sciatic foramen. By cutting the 

 sacro-sciatic ligament on the same side, the sacro-coccygeal part of the 

 spine, with the sacro-iliac joints, will be isolated. Dissect away the 

 inferior ilio-saoral ligament, and remove the skin from the tail. 



The skin of the tail differs from that of the body in general in the 

 greater length of its hairs. On its under surface, however, extending 

 backwards from its root, there is a triangular area without hairs. 

 Along the under surface of the tail, and especially in front, the skin is 

 thin ; but on its upper aspect and sides it is thick, and intimately 

 adherent to the subjacent fascia. 



The muscles of the tail are enveloped by a strong coccygeal fascia 

 which is contimious in front with the inferior ilio-sacral ligament. The 

 isolation of the muscles can be readily effected near the root of the tail, 

 but towards its tip they tend to blend with each other. In each half 

 of the tail there are three muscles, viz., one above, one below, and one 

 at the side. There are also three arteries — one on the middle line 

 below, and one between the inferior and lateral muscles on each side. 

 On each side there are two sets of nerves, one of which accompanies the 

 lateral artery, while the other is on the upper aspect of the bones. 



