Vastus internus. To extend the leg upon the knee: Vastus internus. To flex the leg upon the thigh: Biceps flexor cruris, Semitendinosus, Semitendinosus accessorius, Semimembranosus. To pull the tail down and to one side: Femoro-caudal. To pull the head of the femur backward: Obturator externus. To act as a posterior stay to the head of the femur: Obturator internus. To pull the pelvis forward and to steady it on the head of the femur: Gemellus, Obturator internus, Obturator externus. To extend the metatarsus on the tibia: Gastrocnemius, Soleus, Tibialis posticus. To flex the toes: Peroneus longus, Flexor perforatus medius primus pedis, Flexor perforatus indicis secundus pedis, Flexor perforatus medius secundus pedis, Flexor perforatus indicis primus pedis, Flexor perforans digitorum profundus, Flexor longus hallucis, Flexor perforatus annularis primus pedis. To flex the metatarsus on the tibia: Tibialis anticus. To extend the toes: Extensor longus digitorum, Extensor hallucis brevis. To flex the back laterally and to aid in raising the body. Sacro-lumbalis, Longissimus dorsi. To elevate the tail: Levator coccygis, Levator caudæ. To depress the tail: Depressor caudæ, Infracoccygis. Together— Depressor coccygis, Lateralis caudæ. To pull the tail downward and to one side: Singly— Lateralis coccygis. Depressor coccygis, Lateralis caudæ. To close the eyelids: Orbicularis palpebrarum. To raise the superior eyelid: Levator palpebræ superioris. To pull the lower eyelid downward: Depressor palpebræ inferioris. To pull the membrana nictitans over the eyeball: Quadratus nictitans, Pyramidalis nictitans. To rotate the eyeball: Obliquus superior, Obliquus inferior. To pull the eyeball upward: Rectus superior. To pull the eyeball downward: Rectus inferior. To pull the eyeball outward: Rectus externus. To pull the eyeball inward: Rectus internus. To tense the ear drum: Tensor tympani. To relax the ear drum: Circumconcha. To depress the humerus: Pectoralis major. To raise the humerus: Pectoralis secundus, Pectoralis tertius. Footnote 5: Muscles are arranged in pairs. Singly means one muscle acting alone, _i.e._, without its fellow; together means acting both at the same time. SPLANCHNOLOGY =The Digestive Apparatus.=—This apparatus, apparatus digestorius, consists of the organs directly concerned in the reception of food, in its passage through the body, and in the expulsion of the unabsorbed portion. For convenience, these organs are grouped as follows: the alimentary canal and the accessory organs.