HIP OR GLUTEAL MUSCLES.--The muscles of the hip are very large, filling in around the hip bones. The action of these is much the same as those of the back, as they assist in jumping, running, rearing and in flexing and extending the hind leg. [Illustration: PLATE III. MUSCLES OF THE HORSE--DEEP LAYER--AFTER MEGNIN.] EXPLANATION OF PLATE III. MUSCLES OF THE HORSE. _Deep Layer._ 1. Temporalis. 1. Stylo-maxillaris. 2. Rectus capitis anticus major. 3. Sterno-thyro-hyoideus. 4. Sterno-maxillaris. 5. The Trachea. 6. Scalenus. 7. Splenius. 8. Funicular part of ligamentum nuchæ. 9. Rhomboideus longus. 10. Cervical. 15. Costal serratus magnus. 11. Cartilage of prolongation. 12. Rhomboideus brevis. 13. Transversalis costarum. 14. Longissimus dorsi. 15. Serratus Magnus. 16. External intercostals. 17. Internal intercostals. 18. Rectus abdominis. 19 19. Pectoralis magnus. 20. Postea-spinatus minor. 21. Flexor brachii. 22. Humeralis obliquus. 22´. Caput parvum (of triceps extensor brachii). 23. Extensor suffraginis. 24. Extensor metacarpi magnus divided. 25. Extensor metacarpi obliquus. 25´. Its tendon. 26, 28. Flexor pedis perforans and perforatus. 29. Obliquus abdominis internus. 30. Gluteus maximus. 31. Erector coccygis. 32. Curvator coccygis. 33. Depressor coccygis. 34. Rectus femoris. 35. Vastus externus. 36. Part covered by triceps abductor. 37. Biceps rotator tibialis. 38. Gastrocnemius externus. 39. Plantaris. 40. Flexor pedis perforans. 41. Peroneus. 42. Flexor metatarsi. 43. Extensor pedis (cut across). TAIL OR COCCYGEAL MUSCLES.--Here there are four that are important, one situated on the upper side of the tail when straight out, the action of which is to raise the tail; two, one on each side of the tail, have the power of drawing the tail to either side; the fourth is situated under the tail and is the smallest one of the four. Its action is to draw the tail down. ABDOMINAL MUSCLES.--The abdominal or belly muscles, are four large, flat muscles on each side of the abdomen. The outer edge of these muscles is attached to the outer ends of the false ribs, also to the processes of the lumbar bones and the outer angles of the pelvic or hip bones. They unite below to what is called the linea alba, a hard, white fibrous cord. They pass back in the center of the belly and are attached to the front of the pelvic bones, called the lower bones of the pelvic cavity. About ten inches from where it is attached here, passing forward, is a small slit or hole, which is called the navel, or umbilical opening. Here the navel vessels pass in and out during the foetus life, or before the colt is foaled. This is a point of importance to note, for sometimes at the time of birth this opening does not close and allows the bowels to come down and form what is known as umbilical or navel rupture.