MORPHOLOGY OF THE EXTENSOR MUSCLES. 17 
- §.—Forearm of Myrmecophaga tamandua. (Nat. size.) a@.,anconeus. ez.c.r., extensor carpi radialis (in 
copying the drawing, the lithographer has made the tendon of this muscle appear as if it were 
the continuation of the supinator longus, s.7.). The extensor indicis is seen passing from under 
cover of the ext. minimi digiti and dividing into tendons for the three radial digits.  ex.b.d.m., 
extensor brevis digitorum manus. 
Fig. 9.—Forearm of Hatteria. (24) a., anconeus. «., “nerve to the anconeus.” ew.c.7., extensor carpi 
radialis. s., supinator longus and brevis. 1 and 2, metacarpal heads of deep extensor, cor- 
responding to the thumb and index finger. 5, metacarpal head inserted into the fifth digit. 
. 10.—Diagram of the nerves in the preceding figure. The three roots of the posterior interosseous 
nerve are shown. 
Fig. 11.—Leg of Hatteria. (22) .ew.cr., quadriceps extensor cruris. ezt.c., external condyle of fenur. 
p.n., peroneal nerve. p.t.., posterior tibial nerve. p., peroneus muscle. p.g.dig., peroneus 
quinti digiti. ¢.a., tibialis anticus. 1, tendinous slip from tibialis anticus to phalanx of hallux. 
2, metatarsal heads of deep extensor corresponding to index digit. 3, abductor quarti digiti 
(which can be seen to be plantar in position to the metatarsal heads of the deep extensor). 
Fig. 12.—Diagram of Type Scheme. (1) line of articulation between the humerus or femur and 
the forearm or leg bones. (2) wrist or ankle joint. (3) articulation of carpus or tarsus 
with metacarpus or metatarsus. (4) articulation of metacarpus or metatarsus with phalanges. 
a., triceps or quadriceps. 6. and d., ulnar or fibular sector. f., intermediate sector. c. and By 
radial or tibial sector. I. to V., tendons of the extensor brevis digitorum. (The superficial 
muscles are shown in red, the tendons in blue, and the deeper muscles in black. The metacarpal 
or metatarsal heads are of a darker shade than the rest of the deep extensor. 
Fig. 13.—Forearm of Capybara. (Nat, size.) 
ig- 14.—Leg of Varanus. (14) g.ex.cr., quadriceps extensor cruris. p.n., peroneal nerve. ¢.a., tibialis. 
anticus. 1, slip from tibialis anticus to phalanx of hallux. 2, tibial metatarsal head of ext.br. 2. 
3, fibular metatarsal head of ext.br. 4. 4, abductor quarti digiti. 
Fig. 15.—Forearm of Ornithorhynchus showing the epitrochleo-anconeus. ept.a. (24) m.n., median 
herve. %nt.c., internal condyle of humerus. /i.c.w., humeral head of flexor carpi ulnaris, 
ji.c.w., ulnar head. fi.d., flexor digitorum. 
Fig. 16.—Forearm of Alligator. (Nat. size.) ez.c.d., nerve to extensor communis digitorum cut short. 
x., “nerve to anconeus.” wi.sect., ulnar sector (anconeus) reflected. ext.c., external condyle of 
humerus. (The other letters are explained in the text.) 
Fig. 17.—This figure is copied from Macatister (Zrans. Roy. Irish Acad., Vol. XXV.—Science, 
Pl. XXVI.; Fig. 5), the following description is given in the original:—a. Extensor digitorum 
longus. 0. Tibialis anticus. ¢. Extensor hallucis longus. d. Extensor indicis longus. 
e. Extensor digitorum brevis. jf. Fifth toe slip to last muscle (e). 
Wote.—Certain of the above figures refer to the second part of this Paper. 
