the musculature of the labrum

Compressor muscle of the labrum (fig. i).— An asymmetrical muscle arising in the posterior region of the dorsal wall of the labrum;. Muscle of the hypopharynx (fig. i).-Arises on the tentorial bridge immediately dorsad of muscle 20 and is inserted laterally on the base of the hypopharynx. Flexor of the glossa (fig. 3).—Arises medially at the base of the prementum and is placed on the ventral wall of the labium at the base of the glossa.

NO. 7 MUSCULATURE OF COLEOPTERA DORSEY 7

The flexor muscle of the paraglossa, 2g (fig. 13), arises basally on the ventral wall of the. The ventral muscle of the labium, 21 (fig. 13), originates on the inside of the base of the anterior tentorial arm and is inserted centrally at the base of the prementum. The apparent dorsal muscle of the labium, 20A (fig. 13), arises on the anterior tentorial arm slightly above the ventral muscle of the labium, 21, and.

NO, 7 MUSCULATURE OF COLEOPTERA — DORSEY 9

MUSCLE ARRANGEMENT IN COLEOPTERA

10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3

CARABOIDEA

In Galerita, the dorsal and ventral muscles of the labium, 20 and 21 respectively, are similar to those of Amara.

GYRINOIDEA

The musculature of the labium is essentially the same as that found in Periplaneta, except for the salivary muscles, which are absent in Coleoptera. Silpha americana L., Silphidae (Figures and a specimen of Staphylinae from the group Staphylinidae are the two larval forms used for the study. Muscle IIA (Fig. 34) is an accessory dorsal pharyngeal dilator that probably belongs to the group of dorsal pharyngeal dilator muscles.

NO, 7 MUSCULATURE OF COLEOPTERA — DORSEY 1

HYDROPHILOIDEA

14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 arise on a median apodeme in the posterior gular region; all these

CUCUJOIDEA

An arm extends posteriorly and ventrally from each side of the posterior region of this sclerite to join a heavily sclerotized intralabial brace, the lateral limits of which are the sides of the posterior hypopharyngeal region. The ventral muscle of the labium, 21 (figs.) arises and inserts in the usual way; the dorsal muscle of the labium, 20 (fig. 46), arises in the posterior lateral region of the cibarium, 12, is present, and the muscle of the hypopharyngeal bar Y, 10, is not so violently branched.

BYRRHOIDEA

In the larval Nosodendron (figs), the labral muscles are absent, as is the compressor muscle group of the cibarium, 12. The dorsal muscle of the labium, 20, arises at the posterior end of the anterior tentorial arms and is. The ventral muscle of the labium, 21, originates medially in the posterior region of the postmentum and inserts medially at the base of prementum i.

DRYOPOIDEA

The dorsal dilator muscles of the cibarium, 5, 6 and 7, the muscle of the hypopharyngeal barY,10, and the dorsal dilator muscles of the pharynx, p and 11, are all massive and converge more or less in the region of the posterior region of thecibarium (Figs. 53, 54 ). Bar Y (fig. 54) is large and forms a strong support on the sides of the mouth; it extends ventrally on the sides of the posterior hypopharyngeal region. In Heterocerus the labral, cibarial, pharyngeal and hypopharyngeal muscles are similar to those in Nosodendron; the muscle of the hypopharyngeal bar Y istrifurcate.

NO. 7 MUSCULATURE OF COLEOPTERA DORSEV 1

XL CANTHAROIDEA

ELATEROIDEA

In the first examination it was thought that only the abdominal muscle of the labrium, j (fig. 68, 70), was present, but. The labial and hypopharyngeal muscles are generalized in form, although the ventral muscles of the labium, 21, are. In Chrysobothris the labial and palpal muscles are similar to those of Neotrichophorus; prementum muscle, 22, absent.

SCARABAEOIDEA

75, /6, yy), of the labral muscles only the ventral InPopillia (fig.. 75, /6, yy), of the labral muscles only the ventral muscle of the labrum, j (fig. The cibarial, pharyngeal and hypopharyngeal muscles are similar to those of the generalized plan except that the dorsal dilator muscle of the pharynx, II, is absent. 75, 76) may be homologous with the compressor, muscles of the anterior region of the ciharium, ij (fig. 2), in Periplaneta, or not. ; they are well-developed diagonal muscles placed on the anterior dorsal wall of the cibarium and they seem to have the same function.

The compressor muscle group of the cibarium, 12 (Fig. 75), is broad but not long, and it is. The levator muscle of the labial palpus, 24 (fig. yy), arises on an intralabral torma-like process that extends mesad from the lateroventral base of the labium; this structure extends in a hoop shape dorsally and is. In Macrodactylus the median labial muscle, ^p, is absent; a muscle probably corresponding to the ventral muscle of the labium, 21, of the generalized form, arises rather medially in the anterior region of the postmentum and inserts ventrally on the base of the prementum.

The cibarial, pharyngeal, and hypopharyngeal muscles are similar to those of Popillia; the compressor muscles of the anterior region of the cibarium, ij, are absent, as is the ventral muscle of the labrum, 5. In Lucanus, the median labial muscle, jp, and the ventral muscle of the labrum, 5, are absent; ventral labium muscle, 21, is. The hypopharyngeal rod Y muscle, 10, is large and branched due to the fact that the Y rod has a broad, thin, multibranched distal end, and muscle 10 naturally inserts on these distal branches.

A muscle group possibly homologous to the compressor muscles of the anterior region of the cibarium, Jj, in Popillia is present; the fibers are arranged more longitudinally than diagonally on the dorsal wall of the cibarium, which is true of Popillia.

NO. 7 MUSCULATURE OF COLEOPTERA — DORSEY 21

CLEROIDEA

IO3For the larval stages, Dermestes caninus Germ., Dermestidae, and For the larval stages, Dermestes caninus Germ., Dermestidae and Tenebriodes sp., Ostomatidae, were selected for study. In Dermestes (figs.), the labral muscles are absent; dilator muscle 5 of the cibarhymen, dorsal dilator muscle 11 of the pharynx, and compressor muscle group 12 of the cibarium are also absent. Bar Y (Fig. 84) is heavily sclerotized and forms a rigid lateral support for the dorsal cibarial region and for the mouth.

MELOIDEA

The prementum muscle, 22 (Fig. 95), may be the ventral labium muscle, 21, with its origin displaced anteriorly from the tentorial structure rather than muscle 22, although it is difficult to interpret such a condition. The studied larvae are of the same species as the adults (Figs. 96, 97> 9^) - The musculature is, as the pictures show, well developed and unusual. There is a large, thin, sclerotized apodeme extending ventrally from the center of the middle region of the forehead, on which is the ventral muscle of the labrum, j (Fig. 97), the muscle of the hypopharyngeal bar Y, 10, loA, loB ( Fig. 97), and the dorsal muscle dilator of the pharynx , 11 (fig. 97), all have their own origin.

96, 97), is inserted at the distal end of a modified torma that originates on the ventral labral wall and extends laterally and dorsally. The transverse piece lying beneath the anterior part of the pharynx terminates in the lateral integumental wall of the posterior labial or hypopharyngeal region.

CERAMBYCOIDEA

The dorsal wall of the cibarium is decidedly domed and appears to be able to accommodate the suboral lobe, SL (fig. 99). The dorsal muscle of the labiuin, 20 (fig. 99, loi), is placed laterally on the prementum near the dorsal surface. In the posterior lateral area of the subpharyngeal area, the integument of one side is connected to that of the opposite by a sclerotized intralabial rod, IR (fig. 99).

The suboral lobe (.9L) is probably the hypopharynx; a muscle interpreted as the muscle of the hypopharynx, 19 (fig. 99, loi), is inserted medially at its base. In Prionus the compressor muscle of the labrum, i, is absent; the muscle of hypopharyngeal rod Y, 10, is branched. In the larva Cyllene robiniae (Forst.), Cerambycinae (figs) the muscles are powerful and in the dorsal head area they are usually multi-branched or subdivided.

There is amedianmuscle, 40, under the compressor muscle group of the cibarium, 12 (figs originating medially in the posterior area of the pouch and inserted centrally in the anterior area of the same. By the combined action of muscles y, 11, 12 , and 40 (fig. 104) it would seem as if the lobe formed by the ventral wall of the pouch can draw food into the mouth of the shelf like hypopharynx, HY, which lies immediately. In the ventral head region, the muscle of the hypopharynx, 19, the dorsal and ventral labial muscles, 20 and 21, the ventral and lateral dilator muscles of the pharynx, j?o and 5/.

NO. 7 MUSCULATURE OF COLEOPTERA DORSEY 2$

XVIII. BOSTRICHOIDEA

CHRYSOMELOIDEA

Ill, 112), is branched; the anterior loA branch arises laterally in the anterior frontal area on the posterior surface of the epistomal suture. There is an unusual tendonous structure (fig. 112, TS) arising broadly, medially, and basally from the labial wall of the abdomen; it extends anteriorly to insert medially into the dorsal wall of the labium in the anterior region. A contraction of the dorsal labial muscle, 20 (fig. 112), would exert traction on the labium at the point of insertion; this tendon joining the dorsal anterior labial surface to that of the posterior ventral region probably pulls the anterior labial area when muscle 20 contracts.

There is a heavily sclerotized intralabial strut, IR. fig. 112), in the posterior region of the labium, which ends laterally in the sheath. The latter muscle is inserted on the ventral wall of the labium in an area where the division of the prementum is indistinct; the dorsal and ventral labial muscles, 20 and 21, are inserted at the base. The musculature of Typophorus is similar to that of Leptinotarsa, except that the compressor muscle of the labrum is absent, i.e.

PLATYSTOMOIDEA

CURCULIONOIDEA

The labium is provided with a single pair of muscles (figs., probably corresponding to the inuscle of the prementum, 22, in generalized form. The pharyngeal muscles, 11 (fig. 127), are probably homologous with the dorsal dilator muscles, 11, in the generalized plane, they insert dorsally on the wall of the pharynx posterior to the frontal connective. When the ventral muscle of the labrum, j (Fig. 127), is retracted, the labrum is depressed and the sclerotized dorsal extension, ME, abuts against the posterior inner surface of the epistomal suture (Fig. 127, ES).

When the ventral muscle of the labrum, j, relaxes, the elasticity of the extended process, ME (Fig. 127), pushes the labrum back to its normal position, thus doing the work of the amuscle. A heavily sclerotized intralabial rod, IR (Fig. 127), is present, which terminates laterally on the posterior-lateral walls of the labium and which is connected to the dorsal labial wall adjacent to the mouth opening. The labial muscles agree with those of the generalized form in origin and insertion.

The posterior dorsal margin of the labrum is also provided with the median posterior extension, ME. The muscles of the labrum in the adult (the figs are represented only by the ventral muscle of the labrum, j. A small longitudinal band of muscles,/j (the figs are present; it is possibly homologous with the compressor muscles of the anterior region of the labrum) cibarium , /j.

The hypopharyngeal band Y (fig. 130) is quite large and provides firm support to the sides of the mouth and the posterior lateral cibarial region.

30 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3

SUMMARY

NO. 7 MUSCULATURE OF COLEOPTERA — DORSEY 3I

32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 Heteroderes nicholsi Notman (adult) the ventral muscle of the

NO. 7 MUSCULATURE OF COLEOPTERA — DORSEY 33 Further investigations are necessary to determine the nature of

MUSCLES CONSIDERED IN THIS STUDY

LITERATURE CONSULTED

EXPLANATION OF PLATES

38 SMITPISONIAN MISCELLANEOUS COLLECTIONS VOL. IO3

NO. 7 MUSCULATURE OF COLEOPTERA DORSEY 39

40 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3

NO. 7 MUSCULATURE OF COLEOPTERA — DORSEY 4I

42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. IO3 Plate 21

MUSCULATURE OF COUEOPTERA

MUSCULATURE OF COLEOPTERA

MUSCULATURE OF COLEOPTERA (For explanation of plate see page 38.)

MUSCUUATURE OF COLEOPTERA

128 Musculature of Coueoptera