The alligator and its allies

by A. M. Reese

Muscles of the Posterior Appendages

Ambiens ([Plate III.], Figs. 1 and 2, amb, [Plate IV.], Figs. 2 and 4, amb, [Plate V.], Figs. 2 and 3, amb) (Part I., Rectus femoris and Sartorius partim, Vastus internus, Innere Streckmuskelmasse) (Part II., Gracilis, Rectus femoris, Sartorius). Arises by a short tendon from the anterior spine of the ilium, near its union with the pubis. The muscle swells quickly to a thick belly which, lying under the skin on the forward and inner side of the upper thigh, is again reduced to a small, flat tendon which extends abruptly over the anteromedial surface of the knee joint to its outer side; it then passes through the complex of tendons of the femoro-tibialis muscle, beneath which it unites with the tendon of origin for the peroneus posterior muscle.

To this muscle is the following strange muscle to be ascribed (Part II): it springs, small in extent, from the inner surface of the os pubis near the acetabulum, extends thence forward around the pubis, and runs into a long, thin tendon which unites with the insertion tendon of the subcutaneous extensor ilio-tibialis muscle.

Extensor Ilio-tibialis ([Plate III.], Fig. 2, ex. il. tb.) (Part I., Rectus femoris, Adductor flexor, Glutæus maximus; M. du facia lata, Vastus externus, Tensor faciæ latæ, Tensor femoris vaginæ, Glutæus minimus, Tensor faciæ femoris). This muscle, in the Crocodilia, consists of two parts:

I. The chief part is long and broad, and springs as a tendon from more than the anterior half of the lateral border of the dorsal crest of the ilium, covering the origin of the ilio-fibularis muscle. Its insertion, by a broad, flat tendon, overlying the femoro-tibialis muscle, together with the tendon of this muscle, is on the anterior surface of the head of the tibia.

II. The second, significantly smaller and narrower, part arises outside of the quadratus lumborum by a short tendon from the most dorsal end of the ilium; it goes over, medially, along the nearer head of the ambiens muscle, then to the anteromedial side of the upper leg, into the deeper-lying femoro-tibialis muscle.

Femoro-tibialis ([Plate III.], Fig. 1, fm. tb., [Plate IV.], Fig. 2, fm. tb., [Plate V.], Figs. 1 and 3, fm. tb.) (Cruræus et Vasti, Cruralis). Arises by an anterior inner and a posterior outer head; both heads arise from the outer-anterior and inner surfaces of the femur, and unite with each other and with the extensor ilio-tibialis and ambiens muscles as a strong tendon, which extends over the knee and is inserted on the anterior border of the head of the tibia; this tendon incloses, like a sheath, the end-tendon of the ambiens muscle.

Ilio-fibularis ([Plate III.], Fig. 2, il. fib., [Plate IV.], Fig. 2, il. fib., [Plate V.], Fig. 3, il. fib.) (Biceps cruris, Semitendinosus + Semimembranosus, Glutæus maximus, Abductor fibularis, Flexor abductor cruris). This consists, in the Crocodilia, of two entirely separate small, band-like muscles. The first springs by a short tendon from the lateral surface of the middle ilium, very near the origin of the caudali-ilio-femoralis and extensor ilio-tibialis muscles. The chief part of the end-tendon is inserted at the end of the first sixth of the fibula, on its outer-forward corner near the origin of the peroneus anterior muscle; a shorter tendon-branch goes to the tendon of the peroneus posterior muscle; and a third, still smaller branch goes to the caput femorale of the gastrocnemius muscle, by which it contributes to the structure of the lateral part of the tendo-communis externus.

The second part springs, by an equally short tendon, very near the first, from the hinder end of the dorsal crest of the ilium, goes directly over the preceding to the knee, where its tendon unites with that of the extensor ilio-tibialis muscle.

Ilio-femoralis ([Plate III.], Fig. 2, il. fm., [Plate IV.], Fig. 2, il. fm., [Plate V.], Fig. 1, il. f.) (Glutæus, Quadratus femoris [?], Glutæus medius). This muscle is inwardly fused with the caudali-ilio-femoralis, whose anterior part it forms.

Caudali-ilio-femoralis ([Plate III.], Fig. 2, cd. il. fm., [Plate IV.], Fig. 1, cd. il. fm.) (Zweiter Auswärtsroller, Extensor femoris caudalis accessorius, Glutæus minimus). This forms a thick mass that springs directly from the lateral surface of the anterior and middle parts of the ilium, is covered outside by the ilio-fibularis muscle, and, pushing between the two heads of the femoro-tibialis muscle, is inserted on the whole outer surface of the middle third of the femur.

Caudi-femoralis ([Plate III.], Figs. 1 and 2, cd. fm., [Plate IV.], Fig. 1, cd. fm.) (Pyriformis, Pyriformis + Subcaudalis, Femoro-peroneo-coccygeus, Extensor femoris caudalis). This muscle in the Crocodilia consists of two parts:

I. The chief part extends from the first postsacral (the twelfth) vertebra caudad; it springs from the roots of the caudal ribs (transverse processes) and the whole lateral surface of the vertebral arches. Since the first postsacral vertebra has no ventral process, the muscles of the opposite sides fuse in the mid-line. Towards the caudal region it gradually increases in strength. Its fibers converge in a lateroventral direction to form a short, thick tendon which attaches itself to the inner surface of the femur mediad and somewhat below the trochanter. At right angles from this tendon extends a round, long tendon which, lying parallel to the hinder side of the thigh, pushes in between the chief parts of the ischiadicus and later between the origin-tendon of the gastrocnemius and peroneus posterior muscles, and is inserted on the posterior surface of the head of the fibula.

II. This is a more anterior and inner muscle, small in size, which has a fleshy origin from the bodies and ribs (transverse processes) of the second sacral and first caudal vertebræ at a distance from the posteromedian border of the ischium. It extends caudad, lying near the hinder part of the pubi-ischio-femoralis externus, and is inserted on the trochanter.

Flexor Tibialis Externus ([Plate III.], Figs. 1, 2, 3, fl. tb. ext. or f. t. ext., [Plate IV.], Fig. 4, fl. tb. ext., [Plate V.], Figs. 1 and 3, fl. tb. ext. and f. t. ext.) (Triceps flexor cruris partim, Biceps). A strong, spindle-shaped muscle that arises, together with the ilio-fibularis, by a short tendon, from the side of the portio dorsalis of the ilium, and in the neighborhood of the bend of the knee is split into two tendons, of which the short one is inserted on the fibular side of the neck of the tibia, while the other, running along near the caput femoris of the gastrocnemius muscle, unites with the tendon of the caput tibiæ of the gastrocnemius muscle just beyond the ankle joint.

Flexor Tibialis Internus ([Plate III.], Figs. 1, 2, 3, fl. tb. int., or f. t. int., [Plate IV.], Fig. 4, fl. tb. int., [Plate V.], Fig. 1, fl. tb. int.) (Demi-nerveux + Demi-membraneux, Triceps flexor cruris partim, Gracilis, Adductor flexor tibialis, Semimembranosus, Semitendinosus + Gracilis partim, Gracilis + Semimembranosus + Semitendinosus). A three-headed muscle whose heads arise separately and first unite in the region of the lower leg as a short, strong tendon. Their origins are as follows: (1) As a band from the anterior margin of the ischium, pushing between the ischio-femoralis and the pubi-ischio-femoralis externus muscles; (2) From the posterior margin of the ischium as a narrow, tendinous band near the insertion of the ischio-caudalis muscle; (3) from the portio-dorsalis posterior of the ilium, ventralward, near the origin of the flexor tibialis externus muscle.

Ischio-femoralis ([Plate III.], Fig. 1, is. f.) (Adductores, Adductor longus, Adductor primus). Springs directly (without tendon) from the entire anterior border of the ischium. It is band-like and, running over the tendon of the pubo-femoralis internus and externus muscle, is inserted as a broad, fleshy tendon on the middle third of the inner, posterior surface of the femur.

Pubi-ischio-femoralis Externus ([Plate III.], Fig. 1, p. is. f. int., [Plate IV.], Fig. 1, p. is. f. int.) (as a whole: Quatuor pectinei [partim]; in parts: I. Marsupialis externus, Obturator externus; II. Quadratus femoris). This muscle arises in two parts. The anterior part is broad and comes from the entire ventral and inwardly turned outer surface of the pubis. Its insertion is on the femur in conjunction with the first part of the pubi-ischio-femoralis internus. The second part is shorter but thicker than the first and springs from almost all of the outer surface of the ischium that is not covered by the origins of the ischio-femoralis, pubi-ischio-tibialis, and flexor tibialis internus muscles. It is inserted, by a strong, short tendon, on the trochanter, somewhat caudad to the insertion of the pubi-ischio-femoralis internus.

Pubi-ischio-femoralis Internus ([Plate III.], Fig. 1, p. is. f. int., [Plate IV.], Figs. 1 and 2, p. is. f. int.) (as a whole: Iliacus internus + Quatuor pectinei [partim]; in parts: I. and II.: Kamm-Muskeln, Pectineus inferior [I.] + superior [II.], Marsupialis internus, Obturator internus; III., Iliacus [Darmbeinmuskel], Iliacus internus). This muscle arises by two or three parts: I. The anterior arises, without tendon, from the greater part of the inner and anteriorly directed surface of the pubis; median to this, in the alligator, is a small bundle, II., which unites with part I. These unite with the pubi-ischio-femoralis externus to form a strong tendon that is inserted on the trochanter.

III. This is a larger muscle that springs without tendon from the inner surface of the body and transverse processes of the twenty-fifth and twenty-sixth (in alligator) vertebræ, from the part of the ilium that lies between these transverse processes and the ischium, and from a small part of the ischium. It is inserted on the whole inner surface of the proximal third of the femur.

Pubi-ischio-femoralis Posterior ([Plate III.], Fig. 1, p. is. f. post., [Plate IV.], Figs. 1 and 4, p. is. f. post. and pb. is. f. m. post.) (Adductus [partim], Gemellus, Obturator internus). Springs without tendon from the whole caudally directed border of the ischium. It is inserted, by a short tendon, near and laterad to the tendon of the ischio-femoralis muscle, on the hinder surface of the upper leg.

Extensor Longus Digitorum ([Plate V.], Figs. 2 and 3, ext. l. [long.] dig.) (Long extenseur commun, Gemeinschaftlicher Fussheber oder Beuger, Extensor communis digitorum). Springs, together with the tibialis anticus, from the external condyle of the femur, goes with this muscle under the ligamentum tibio-fibulare and after union with this divides into four short tendons. Three of these tendons are inserted on the fibular side of the bases of the first three metatarsal bones; the fourth goes over into the muscle of the third toe.

Tibialis Anticus ([Plate III.], Fig. 1, tib. ant., [Plate IV.], Fig. 4, tib. ant., [Plate V.], Figs. 2 and 3, tib. ant.) (Jambier antérieur, Vorderer Schienbeinmuskel). Springs by a fleshy tendon from the anterior surface of the head and neck of the tibia and quickly unites with the following muscle.

Peroneus Anterior ([Plate V.], Figs. 2 and 3, peron. ant.) (Peroneus longus). In the alligator. Its origin: it extends from the insertion of the ilio-fibularis muscle distalwards by the whole outer surface of the fibula, under the skin and over the ligamentum tibio-fibulare, and gives off a broad, tendinous portion to help strengthen the tendon Achilles, which portion may be followed to the rudiment of the fifth toe. On the outer side of this toe rudiment is attached a tendon from the tibial border of the muscle.

In the crocodile. This muscle is here divided into two parts, of which the one that springs from the anterior surface of the fibula is inserted on the toe rudiment, while the greater and outward part extends over the calcaneum bone and has the same distribution as in the alligator.

Peroneus Posterior ([Plate IV.], Figs. 3 and 4, peron. post., [Plate V.], Figs. 2 and 3, peron. post.) (Plantaris). Springs chiefly from the tendon of the ambiens muscle running over the knee and forms the direct continuation of this muscle. Besides this come tendinous fibers from the insertion tendons of the femoro-tibialis and extensor ilio-tibialis muscles; and finally supporting fibers from the outer, end-tendon of the ilio-fibularis muscle. The fibers of this muscle pass partly into the fibular portion of the caput femoralis of the gastrocnemius, while the chief mass of the muscle is inserted on the posterior surface of the calcaneum.

Gastrocnemius ([Plate III.], Figs. 1 and 3, cap. int. gastr., [Plate IV.], Fig. 4, cap. int. gastr. and cap. ext. gastr., [Plate V.], Figs. 2 and 3, cap. ext. gastr. and cap. int. gastr.) (Solenmuskel, Outer head of gastrocnemius). This is the strongest superficial flexor muscle on the posterior surface of the lower leg; it consists of two heads: I. The caput femorale (externum) originates by a strong, short tendon from the lateral and posterior surface of the external condyle of the femur. This head has a double insertion: (1) from the outer, fibular border of the muscle separates off a tendon that spreads out in the first layer of the plantar tendon-muscle; (2) the chief part of caput I. becomes a broad, flat, subcutaneous tendon which is covered by the tendon Achilles and serves as the origin of the short flexors of the toes.

II. The caput tibiale (internum) springs without a tendon from the posterior surface of the head and the proximal third of the tibia. The broad and somewhat flat muscle has two insertions: (1) on the plantar and medial border of the first basis metatarsi; (2) the chief insertion on the outer border of the rudimentary fifth toe, after forming, with the tendon of the flexor tibialis externus, the tendon Achilles.

Flexor Longus Digitorum ([Plate IV.], Fig. 4) (Langer durchbohrender gemeinschaftlicher Zehenbeuger). A many-headed muscle visible on the posterior side of the lower leg after removal of the preceding muscle. (a) Caput externum: a flat, fairly broad muscle which springs from the outer and posterior surface of the fibula. Arriving at the astragalo-scaphoid bone, it forms a very strong tendon which unites with the still stronger tendon of the other head and both together form the broad initial tendon of the flexor digitorum communis brevis muscle. (b) Caput internum: this springs without a tendon from the whole posterior surface of the upper half of the tibia, sometimes, as in crocodiles, uniting with the caput femoralis of the gastrocnemius muscle. The common tendon splits into three points for the first, second, and third toes.

Tibialis Posticus ([Plate V.], Fig. 2, tib. post.) (Jambier postérieur, Hinterer Schienbeinmuskel). Originates without tendon from the whole fibular side of the tibia, on the one hand, and from the whole inner and forward side of the fibula on the other hand, occupying the whole space between these two bones on the hinder side of the lower leg. At its proximal end it is united with the caput internum of the preceding muscle which completely covers it from behind. It narrows down to a very strong tendon which divides into two equally strong, round tendons; of these the one on the tibial side is inserted on the basis ossis of the first metacarpal, the one towards the fibula goes immediately to the second metacarpal.

Interosseus Cruris (Kniekehlmuskel). A small muscle stretching between the distal ends of the fibula and tibia with almost transverse fibers; it is covered dorsally by the tibio-fibulare ligament and appears as a distal division of the tibialis posticus muscle.

Flexor Digitorum Brevis (Flexor longus accessorius, Flexor brevis perforatus). Springs from the bones of the foot and from the strong tendon of the flexor digitorum longus muscle. It divides into three bellies for the second, third and fourth toes. The first two are pierced by the above-mentioned tendon of the flexor digitorum longus and are inserted on the next to last phalanx of the second and third toes; the third, on the contrary, is inserted on the claw joint of the fourth toe and is not perforated; there is no tendon to the fourth toe from the flexor digitorum longus muscle.

Extensor Hallucis Proprius ([Plate V.], Fig. 3) (Kurzer gemeinschaftlicher Zehenstrecker, Extensor hallucis). This muscle springs by a short, flat, fairly strong tendon from the outer dorsal border of the distal half of the fibula. It is inserted: (1) on the proximal half of the first metatarsal bone, (2) a second much weaker part is united with the tendon of insertion of the tibialis anticus extensor longus digitorum to the first metatarsal bone.