MUSCULATURE. 267 
More laterally, fibers arise from the articulating processes of the sacral 
vertebrae, and from the posterior part of the ilium and lateral part of the ver- 
tebrae. These fibers become partly tendinous as they pass dorsocaudad to 
insert on the dorsal parts of the posterior caudal vertebrae. This muscle is 
the extensor caudae lateralis. 
Other and more numerous fibers arise similarly from the posterior margin 
of the ilium and the dorsal parts of the vertebrae ventral to the articulating 
processes. The muscle-mass thus formed appears to correspond in part to the 
abductor caudae externus. It passes back along the dorsolateral side of the 
tail and sends tendons to the anterior margins of the transverse processes of 
the vertebrae. 
The ventral musculature of the tail consists of two main masses, a lateral 
and a medial, on each side. The former is from muscle fibers arising from the 
posterodorsal part of the ischium and from the ventral side of the caudal verte- 
brae adjacent. It forms a tapering bundle inserting by tendinous fibers into 
the ventral part of the transverse processes. It is probably the homologue 
of the coccygeus. 
The more medial masses of muscles arise along the length of the sacral 
and caudal vertebrae on either side of the median line as a series of bundles 
that taper posteriorly. They insert by muscle fibers on the ventral part of the 
coecygeal vertebrae and by strong short tendons that pass to each of the chey- 
ron bones. This muscle-mass is probably homologous with the flexor caudae 
longus and the flexor caudae brevis. 
From the transverse process of the third caudal vertebra a narrow band 
of muscle passes ventrally, beneath the rectum to join a similar muscle from 
the opposite side. They together form a muscle that probably corre- 
sponds to the levator ani. A few muscular fibers join this muscle to the 
preceding. 
MUSCLES OF THORAX AND ABDOMEN.— The sternomastoideus originates 
by muscular and tendinous fibers from the midventral part of the broad lobe 
of the episternum. Proximally the muscle is flat and broad (about 20 mm. 
transversely) and is united by fascia to the corresponding muscle of the opposite 
side. It tapers as it passes forward to its insertion by a stout tendon at the 
mastoid region, just above the ear. 
The pectoral muscles are essentially as in the Echidna. The ectopectoralis 
arises from the side of the manubrium beneath the origin of the sternomastoideus, 
and inserts by tendon on the pectoral ridge of the humerus. <A second portion, 
corresponding to an entopectoralis is rather clearly distinguishable, arising 
