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Show 1903.] THE MUSCLES OF THE UNGULATA. 291 to the 6th or 7th caudal vertebra, while the former runs to the tip of the tail. The Inter spin ales and Intertransversales caudce are feebly developed and diminish as the bones decrease in size. A DDENDUM. Orbital Muscles.-In addition to the recti and obliqui of human anatomy, there is a retractor bulbi or posterior rectus which surrounds the optic nerve and is inserted into the posterior part of the eyeball. This in the Chevrotain (20, 21) is divided into an upper and lower part, while in the Horse (63) and Ass (69) the division is more complete, for it is divided into four slips corresponding to the four recti. In the Horse (63) and Ass (69) there is also a middle oblique muscle which rises from the inner wall of the orbit below the pulley and later on joins the superior oblique ; it is apparently a part of this muscle which does not pass through the pulley. W e have looked, for this muscle in the Artiodactyla but have never seen it, nor do we know whether it occurs in the Rhinoceros and Tapir among the Perissodactyla. GENERAL SUMMARY. W e now propose to consider whether a study of these muscles is of any value from a classificatory point of view, and it will perhaps be best to collect first those myological points which are common to all Ungulates though not common to all mammals. Myological Characteristics of the Ungulata. 1. Almost constant presence of masto-styloideus. 2. Absence of epitrochleo-anconeus. 3. Rudimentary condition of pronator radii teres. 4. Absence of pronator quadratus (except in Tapir). 5. Position and function of extensor carpi ulnaris as a flexor of the carpus. 6. Absence of supinator brevis. 7. Insertion of caudo-femoralis into patella. 8. Semi- and presemimembranosus fused almost to insertion. 9. Marked expansions from hamstrings to calcaneum forming a sheath for the tendo Achillis. 10. Only an ischial origin for the biceps femoris. 11. Usual absence of bicipiti accessorius. 12. Constant presence of straight and reflected heads to rectus femoris. 13. Usual presence of femoral origin of tibialis anticus (Subungulata the exception). 14. Usual presence of femoral origin of extensor longus digitorum (Elephant the exception). 15. Peroneus longus can be traced up to femur with external lateral ligament. 19* |