MORPHOLOGY OF THE EXTENSOR MUSCLES. 15 
of the short extensor of reptiles; its position, connections, and innervation show 
this to be the case. 
Hind Iimb.-—-We have seen that in Hatteria the intermediate sector of the 
superficial stratum has retained its hold on the fibular condyle of the femur, 
and that the tibial and fibular sectors arise from the bones of the middle segment, 
A very similar condition is retained in some of the Mammalia, e.g., Hyxax capensis.* 
Tn Man, as in Ornithorhynchus, all three sectors have lost their hold on the femur. 
Fibular sector.—The undivided peroneus of Hatteria has split into peroneus longus 
and brevis. The tendon of the former has wandered across the sole to the inner 
side of the foot.+ The peroneus brevis has retained the primitive attachment to the 
base of the fifth metatarsal bone, and not infrequently sends a tendon to the 
phalanges of the minimus (peroneus quinti digiti). This tendinous slip, in rare 
cases, becomes continuous with a fifth belly of the ext. brevis digitorum, and thus a 
condition greatly resembling the disposition in Hatteria becomes developed (see 
Fig. 11, p.q.dig.). Tibial sector.—The tibialis anticus is essentially similar to the 
muscle thus named in Hatteria. It is inserted into the internal cuneiform and 
into the base of the first metacarpal bone, and in rare cases it sends forward a slip to 
the paroximal phalanx of the hallux,; presenting a condition evidently homologous 
to the slip from the tibial sector to the hallux in Hatteria (Fig. 11, 1). Inter- 
mediate sector.—The ext. longus digitorum occupies a very much more distal 
position than in Hatteria. It arises slightly from the tibia and from almost the 
entire length of the fibula. It is inserted into the phalanges of the four other toes. 
A fifth tendon (peroneus tertius) is inserted into the metagarfal bone of the little 
toe. This, probably, represents a reversion to the more primitive metatarsal attach- 
ment. 
Deep stratum.—The extensor brevis digitorum very obviously corresponds to the 
muscle thus named in Hatteria. The belly which supplies the little toe, however, 
is absent in the great majority of cases in the human subject; it may, however, 
appear as a variety.§ The extensor ossis metatarsi hallucis, which is so well repre- 
sented in the upper limb of Man, has completely disappeared as a normal arrange- 
ment in the lower limb, but appears in rare cases as a variety.|| The extensor 
proprius hallucis has divided into two parts. One portion has extended its origin 
further up the leg than in Hatteria, and has become the extensor longus hallucis. 
* Mivart and Muriz. Proc. Zool. Soc., 1865, p. 349. 
+t Rug has traced this migration of the tendon of the peroneus longus. (Op. cit., pp. 594 and 598.) 
¢{ Macauister. Trans. Roy. Irish Acad., Vol., XXV.—Science ; p. 124. 
§ Macauister. Op. cit., p. 126. Tusrur. Les Anomalies Musculatres chez VHomme. Paris, 1884, 
p. 724. 
|| Macatister. Op. cit., p. 123. Trsrur. op. cit., p. 730. 
