THE FROG 49 
tween the adductor magnus and the gracilis major. It arises by 
two heads; the anterior head passes through a slit in the adductor 
magnus and unites with the posterior head in the distal third of 
the thigh; its tendon of origin gives attachment to a small slip 
which belongs to the adductor magnus. 
2. The leg (crus). The gastrocnemius lies along the flexor sur- 
face of the tibio-fibula, forming the calf of the leg. Its origin is 
by two heads; distally the muscle ends in the strong tendon of 
Achilles. Divide and reflect the gastrocnemius. 
The tibialis posticus lies between the gastrocnemius and the 
tibio-fibula. 
The tibialis anticus longus lies along the extensor surface of 
the tibio-fibula. It is a slender muscle which divides posteriorly 
into two slips. 
The peroneus lies on the postaxial side of the leg, between the 
tibialis anticus longus and the gastrocnemius. 
The extensor cruris is a small muscle lying on the preaxial side 
of the anterior half of the tibialis anticus longus. Divide and 
reflect the latter; this will.expose: 
The tibialis anticus brevis. The body of this muscle lies im- 
mediately beneath the preaxial slip of the tibialis anticus longus. 
XV. CONNECTIVE TISSUE. 
Connective tissue serves to unite the various elements of an 
organ, binds together muscle fibers, and forms tendons and liga- 
ments. There are several varieties of connective tissue, which 
agree in that the intercellular substance is large in amount. 
Examples of connective tissue have already been encountered in 
the study of cross-sections of various organs, particularly the 
alimentary canal and the skin. For more careful study con- 
nective tissue should be prepared as follows: From a preserved 
specimen cut out a small piece of the white fibrous connective 
tissue which binds the skin to the body, spread it out on a slide 
in a drop of water, and cover it with a cover glass. Under high 
power observe the numerous fibers, which are usually unbranched 
and of a characteristic wavy appearance. Irregularly distributed 
among the fibers are the connective tissue corpuscles or cells; 
these have conspictious granular nuclei and vary considerably in 
