162 
PROFESSOR A. MACALISTER ON THE 
longus; the long head crosses the shoulder-joint, with which its bursal sheath freely 
communicates; the two parts of this muscle join inseparably. The brachialis anticus 
is large, and extends as high as the neck of the humerus on its outer side. There are 
two coraco-brachiales : a coraco-brachialis longus (Wood), extending for the lower half 
of the bone, even to the inner condyle, and a brevis, thick and iieshy, closely applied to 
and crossing over the subscapularis tendon. 
The pronator teres extends for the upper half of the radius ; the flexor carpi radialis 
has no second head, and a single tendon inserted as usual ; there is no palmaris longus. 
The flexor digitorum is in three parts, two of which are condyloid and one ulnar. The 
flexor pollicis has a radial origin, but it unites with the three parts of the flexor digi- 
torum, and I could only detect one set of tendons. There is a very small rudiment of 
a pronator quadratus, consisting of a few fibres overlying the part where the forearm- 
bones are united together below; these are traceable in the lower third of the forearm. 
The supinator longus extends from above the outer condyle to the lower end of the 
radius. The extensor carpi radialis has a single belly with two tendons ; there is no 
extensor minimi digiti, an extensor ossis metacarpi pollicis, and an extensor indicis ; 
the other forearm-muscles display no features of interest. 
In the hinder limb of the Flying Squirrel the muscular arrangements are as follows. 
The gracilis is thin and narrow, the adductor mass is divisible into the following parts : — 
pectineus (small and round), adductor longus (with a narrow tendinous origin), adductor 
magnus condyloideus (closely connected to the semimembranosus), adductor magnus 
superior, and adductor brevis, all quite distinctly separable. The hamstrings are; — 
semimembranosus, large and fleshy, attached to the upper sixth of the inner edge of the 
tibia ; semitendinosus, with two heads, one arising under the last from the tuber ischii, 
the other, as in the Beaver, from the spine of the first caudal vertebra, at first lying 
superficial to the biceps ; both uniting, are inserted below the semimembranosus by a 
tendinous expansion for nearly the second fourth of the inner side of the tibia ; biceps 
is triangular, arising narrow from the tuber ischii, and inserted into the outer and upper 
third of the leg. 
Agitator caudse passes from the two foremost caudal spines, and is inserted into the lower 
half of the outer side of the femur on its flexor aspect, as far as the outer condyle. 
Gluteus maximus arises from the sacral spines, and from that of the first caudal ver- 
tebra; it is inserted into the third trochanter. Tensor vaginse femoris is moderately 
thick, and extends to the upper half of the outside of the femur, being inserted into the 
fascia as usual ; its origin is from the iliac crest. The gluteus medius is thick and sepa- 
rate from the largely developed pyriformis. Gluteus quartus is distinct, marginal, and 
anteriorly inserted. Xliacus is small, separate from the large psoas magnus; and the 
psoas parvus is thin and flat. The quadriceps extensor cruris consists of a large rectus 
with a single iliac origin, an equally large vastus externus, and vastus interims and 
crureus, partially separable. The tibialis anticus is twice the size of the extensor digi- 
torum, and is single ; neither muscle rises to the femur. 
