218 NATURAL HISTORY SOCIETY OF DUBLIN. 
lower half of the radius in the three-toed sloth, in which its insertion 
is split into two parts—a lower, extending to the front of the carpal 
end of the radius, and to the anterior ligament of the wrist joint; and 
an upper, which is attached to the lower half or sometimes two-thirds 
of the radius. It is attached nearly to the upper half of the radius for 
a variable extent in the kangaroo and wallaby, but to the middle-third 
in Perameles, Didelphys, and Phalangista. It occupies more than two- 
thirds of the radius in Iguana (Mivart, “‘P. Z. 8.,’’ 1867, p. 783); and in 
the alligator and crocodile it is attached nearly to the entire length of 
the radius, as is likewise the case in the green lizard; while in the 
Greek tortoise it is attached to the lower third of the radius only. 
The second pronator normally developed is the short, nearly trans- 
verse ulno-radial muscle; the pronator quadratus, which, when per- 
fectly developed, occupies the entire anterior surface of these bones 
from elbow to wrist joint. This muscle is most largely developed in 
the dog, in which it occupies the entire interosseous space from the 
elbow to the wrist; and a similar development occurs in the allied 
forms, the dingo, fox, wolf, and hyena, also in the wallaby and Pe- 
rameles among Marsupials. Rarely, however, is this muscle developed 
as an unbroken, continuous sheet, but it is much more commonly the 
subject of either of two modifications—either becoming diminished 
from above downwards, and shrinking to smaller dimensions, or else 
being parted into two in the centre, and remaining in the form of upper 
and lower separate muscles; the former of these varieties occurs in by far 
the largest number of animals—thus, in the giant kangaroo, it shrinks to 
the lower two-thirds of the forearm; in the tiger, lion, cat, opossum, 
porcupine, and civet cat, it occupies about one-half; in the Virginian 
bear, racoon, agouti, and marmot, it extends for about one-third; in 
man, most monkeys, apes, and lemurs, the coati, paradoxure, the brown 
bear, the otter, and marten, it occupies about one-fourth ; it is very 
small and rudimentary in the three-toed sloth, the Orycterope,* and the 
seal, occupying in these from one-fifth to one-sixth of the forearm 
bones. In the last-named animal, Carus and Duvernoy mention it as 
non-existent. Prof. Haughton does not refer to it, and twice I have 
looked for it in vain. Meckel and Humphry, however, describe it as 
present, and I found it in a third seal. 
The second and more interesting variety of this muscle is the form 
found in man and reptilia, in which the short pronator becomes deficient 
in the centre, leaving its upper and lower ends persistent. This con- 
dition is most perfectly to be traced in saurian reptiles, where a short 
upper pronator underlies the median nerve; in some cases, as in the 
green lizard, closely connected to the true quadrate pronator. This 
muscle is sometimes, in origin, promoted above the ulna to the inner 
ligament of the elbow, as in the chameleon, or to the inner condyle, as 
* Mr. Galton, ‘ Trans. Lin. Soc.,” vol. xxvi., p. 5, describes this muscle as larger in 
Orycteropus than I have mentioned above. 
