1901.] THE MUSCLES OE THE TNGULATA. 667 



tendon is present but unattached to the hyoid. Bronn (VI.) says 

 that the anterior bellies are always connected with one another in 

 E-uminants ; and Chauveau (TI.) describes a small square muscle in 

 the Ox \yhich passes transversely across, uniting the two digastrics 

 by passing beneath the base of the tongue. Our own experience, 

 based on the Ox (36), Sheep (42, 43, 45), and Duiker-bok (49), 

 shows us that this union across the middle line is not a charac- 

 teristic mark of the Bovidse as a family. 



In the Tapiridae (52, 52 a, 54) the muscle is very strong and is 

 inserted into the posterior half of the lower border of the mandible, 

 but there is no central tendon at all. 



In the Equidae (56, 57, 58, 61) the muscle divides immediately 

 after its origin from the paroccipital ; one part goes to the border 

 of the ramus of the mandible just above the angle, while the other 

 forms the normal posterior belly of a typical digastric and is sepa- 

 rated from the anterior belly by a definite central tendon. The 

 insertion of the anterior belly is a good deal nearer the symphysis 

 than it is in most other Ungulates. Among the Subungulata the 

 Hyrax (67, 68) has the origin of the digastric chiefly from the 

 paramastoid ; as it goes forward the muscle spreads out like a fan 

 to be inserted into the greater part of the lower margin of the 

 body of the mandible from the angle forward. About two thirds 

 of the way from the origin is a narrow zigzag tendinous streak, 

 the only representative of a central tendon. 



In the Indian Elephant (73, 74, 75, 76, 77) the muscle runs 

 from the paroccipital to the jaw in front of the angle, but there 

 is some cliiference of opinion about the central tendon. Mayer 

 (XXVIII.), Watson (XXX.), and Young (XXXI.) foiuad one, but 

 Miall and Grreenwood (XXIX.) and Cuvier and Laurillard (I.) did 

 not see it. Miall and Greenwood's description seems somewhat 

 complicated, but we have little doubt that they have included the 

 stylo-hyoid and masto-styloideus with the digastric. 



From the foregoing description it will be seen that the digastric, 

 as in other orders, is of some classificatory importance : thus in the 

 Hippopotamus and Suidse the posterior belly is often suppressed. 

 In the Tapiridae the central tendon is absent. In the Hyracoidea 

 it is a mere zigzag streak. In the Elephantidae it may be present 

 or absent. In the Equidae a part of the posterior belly is inserted 

 into the ramus of the jaw, while in the Cervidae the tendon is 

 better developed than in any other family. 



Muscles attached to the Hyoid Bone. 



Mylo-hyoid. — This muscle has the usual attachments, though it 

 does not in all cases run forward as far as the symphysis ; this is 

 especially seen in the Suidae (11, 12, 14). In the Elephant, Miall 

 and Greenwood (74) say that the muscle is attached to the great 

 cornu of the hyoid and to a tendinous arch which crosses the thyro- 

 hyoid membrane. Chauveau (II.) and Lesbres (V.) notice that in 

 Euminants two planes are found, and our own dissections bear this 



