Comments on the evolution of the jaw adductor musculature of snakes

The aim of this study is to provide a general view of the adductor musculature of the alethinophidian snakes. The aponeurotic system present in anilioid snakes is here described as being also present in colubroid and booid snakes. Although modified in various groups, this aponeurotic system retains the same topographical pattern in the anilioids, booids and colubroids, and is thus hypothesized to be homologous. An analysis of the aponeurotic system and related muscular bundles within the alethinophidian snakes is given. A new terminology is proposed for the jaw adductor muscles where the muscles levator anguli oris and adductor mandibulae externus superficialis (proper) of snakes (sensu Lakjer, 1926; Haas, 1962) retain these names even if this fails to reflect the presumed homologies with the bundles of the same name in lizards (see Rieppel, 1988b); the fibres originating from the temporal tendon in the Anilioidea, and presumed to form a bundle of composite nature (Rieppel, 1980b), are named the M. adductor mandibulae externus temporalis (lost by the Macrostomata); the M. adductor mandibulae externus medialis is a composite muscle in the Anilioidea (Rieppel, 1980b) which give rise to two different muscles in the ‘booids’, the M. adductor mandibulae externus medialis, pars anterior and the M. adductor mandibulae externus profundus, the former being secondarily lost by the Caenophidia which retains only fibres homologues of the 3b and 3c heads of the profundus layer of lizards; the so-called M. adductor mandibular externus profundus of snakes (sensu Lackjer, 1926; Haas, 1962) is also a composite muscle in the Anilioidea (Rieppel, 1980b), in the alethinophidians it is essentially made of fibres homologous with the posterior pinnate part of the medialis layer of lizards, and is here named the M. adductor mandibulae externus medialis, pars posterior. As a result from this analysis it follows that: (1) the Macrostomata are characterized by the downward extension of the fibres forming the M. adductor mandibulae externus medialis, pars anterior and the loss of the M. adductor mandibulae externus temporalis: (2) the Xenopeltidae are set apart from the remaining macrostomatan snakes by the retention of the M. levator anguli oris and of a well developed lateral sheet of the quadrate aponeurosis; (3) the ‘booids’ form a monophyletic group comprising only the Boidae and Bolyeriidae (with the exclusion of the Xenopeltidae and Tropidophiidae) which is characterized by a differentiated M. adductor mandibulae externus medialis, pars anterior inserting on the lateral surface of the compound bone via its own aponeurosis; (4) the Tropidophiidae are set apart from all other snakes by the peculiar course of their lateral head vein; however, they belong to the Caenophidia as they show a facial carotid artery which passes dorsally to the mandibular and maxillary branches of the trigeminus; (5) a possible additional character in favour of an Acrochordoidea + Colubroidea monophyletic unit may be given by the pattern of innervation of the jaw adductor muscles in these two taxa; (6) a new interpretation of the compressor glandulae muscular complex of Atractaspis resulted in a morphologically similar pattern to that of the viperids; the phylogenetic implications of such similarity are discussed in detail.     

Ontogeny of the jaw and maxillary barbel musculature in the armoured catfish families Loricariidae and Callichthyidae (Loricarioidea,Siluriformes), with a discussion on muscle homologies

The neotropical loricarioid catfishes include six families, the most species‐rich of which are the Callichthyidae and the Loricariidae. Loricariidae (suckermouth armoured catfishes) have a highly specialized head morphology, including an exceptionally large number of muscles derived from the adductor mandibulae complex and the adductor arcus palatini. Terminology of these muscles varies among the literature, and no data exist on their ontogenetic origin. A detailed examination of the ontogeny of both a callichthyid and a loricariid representative now reveals the identity of the jaw and maxillary barbel musculature, and supports new hypotheses concerning homologies. The adductor mandibulae muscle itself is homologous to the A1‐OST and A3′ of basal catfishes, and the A3′ has given rise to the newly evolved loricariid retractor veli as well. The A2 and A3″ have resulted in the retractor tentaculi of Callichthyidae and the retractor premaxillae of Loricariidae. Thus, these two muscles are shown to be homologous. In Loricariidae, the extensor tentaculi consists of two separate muscles inserting on the autopalatine, and evidence is given on the evolutionary origin of the loricariid levator tentaculi (previously and erroneously known as retractor tentaculi) from the extensor tentaculi, and not the adductor mandibulae complex. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 76–96.     

Homologies among different adductor mandibulae sections of teleostean fishes, with special regard to catfishes (Teleostei: siluriformes)

The adductor mandibulae complex has been a subject of discussion and uncertainties due to a wide range of differentiations and fusions that have occurred during teleost evolution. The adductor mandibulae of numerous catfishes was studied in detail and compared with that of several other teleosts described in the literature. Our observations and comparisons demonstrate that: 1) the adductors mandibulae Aomega, A2, and A3 of acanthopterygians correspond, respectively, to the Aomega, A2, and A3 of ostariophysines; 2) the antero-dorso-lateral (A1) and the antero-ventro-lateral (A1-OST) sections of the adductor mandibulae present, respectively, in acanthopterygians and in basal ostariophysines are the result of two different patterns of differentiation of this muscle; 3) some derived ostariophysines present a lateral section of the adductor mandibulae attached to the upper jaw (A0) that is not homologous with any other section of this muscle present in any other ostariophysine or acanthopterygian fish; 4) the configuration of the adductor mandibulae present in Diplomystes seems to be the plesiomorphic condition for catfishes; and 5) the muscle retractor tentaculi, present in a large number of catfishes, is derived from the inner section of the adductor mandibulae (A3) and, thus, is not homologous with the lateral bundle of this muscle (A0) that inserts on the upper jaw in some derived ostariophysine fishes.     

Comparative myology of the mandibular and hyoid arches of sharks of the order hexanchiformes and their bearing on its monophyly and phylogenetic relationships (Chondrichthyes: Elasmobranchii)

The order Hexanchiformes currently comprises two families, Chlamydoselachidae (frilled sharks) and Hexanchidae (six‐ and seven‐gill sharks), but its monophyly and relationships with other elasmobranchs are still discussed. Previous studies of hexanchiforms addressing these issues were based mainly on external morphology, teeth, skeletal features, and molecular data, whereas the employment of characters derived from variations in muscles has not been significantly explored. Dissections of four species of Hexanchiformes (including Chlamydoselachus anguineus) are reported here describing the mandibular (musculus adductor mandibulae dorsalis, m. adductor mandibulae ventralis, m. levator labii superioris, m. intermandibularis, and m. constrictor dorsalis) and hyoidean (m. constrictor hyoideus dorsalis and ventralis) arch muscles. Our results provide new data concerning the relationships of hexanchiforms to other elasmobranchs. The m. adductor mandibulae superficialis is described and illustrated in C. anguineus, contradicting previous accounts in which is was considered absent. The anteroposterior orientation of the m. adductor mandibulae superficialis in Chlamydoselachus is similar to the pattern found in hexanchids, squaloids, and hypnosqualeans (including batoids), suggesting it was secondarily lost in Echinorhinus. This muscle therefore provides further support for the inclusion of the Chlamydoselachidae and Hexanchidae in the Squalomorphi, and not basal to all other elasmobranchs or nested within an all‐shark collective, as has been previously proposed. However, the m. adductor mandibulae superficialis originating at the jaw joint and with an aponeurotic insertion in hexanchids, squaliforms, and hypnosqualeans, may be a separate derived feature uniting these taxa. The insertion of the m. constrictor dorsalis is restricted to the postorbital articulation in hexanchids, whereas it extends farther anteriorly in C. anguineus. The insertion of the m. constrictor hyoideus dorsalis solely on the palatoquadrate is found exclusively in the Hexanchidae. We conclude that no specific pattern of mandibular or hyoid arch muscles support the monophyly of hexanchiforms (i.e., including Chlamydoselachus). J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Cranial muscles of the anurans leiopelma hochstetteri and ascaphus truei and the homologies of the mandibular adductors in lissamphibia and other gnathostomes

The frogs Ascaphus truei and Leiopelma hochstetteri are members of the most basal lineages of extant anurans. Their cranial muscles have not been previously described in full and are investigated here by dissection. Comparison of these taxa is used to review a controversy regarding the homologies of the jaw adductor muscles in Lissamphibia, to place these homologies in a wider gnathostome context, and to define features that may be useful for cladistic analysis of Anura. A new muscle is defined in Ascaphus and is designated m. levator anguli oris. The differences noted between Ascaphus and Leiopelma are in the penetration of the jaw adductor muscles by the mandibular nerve (V³). In the traditional view of this anatomy, the paths of the trigeminal nerve branches define homologous muscles. This scheme results in major differences among frogs, salamanders, and caecilians. The alternative view is that the topology of origins, insertions, and fiber directions are defining features, and the nerves penetrate the muscle mass in a variable way. The results given here support the latter view. A new model is proposed for Lissamphibia, whereby the adductor posterior (levator articularis) is a separate entity, and the rest of the adductor mass is configured around it as a folded sheet. This hypothesis is examined in other gnathostomes, including coelacanth and lungfish, and a possible sequence for the evolution of the jaw muscles is demonstrated. In this system, the main jaw adductor in teleost fish is not considered homologous with that of tetrapods. This hypothesis is consistent with available data on the domain of expression of the homeobox gene engrailed 2, which has previously not been considered indicative of homology. Terminology is discussed, and “adductor mandibulae” is preferred to “levator mandibulae” to align with usage in other gnathostomes. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Jaw movement kinematics and jaw muscle (EMG) activity during drinking in the pigeon (Columba livia)

Summary Movements of the maxilla and mandible were recorded during drinking in the head-fixed pigeon and correlated with electromyographic activity in representative jaw muscle groups. During drinking, each jaw exhibits opening and closing movements along both the dorso-ventral and rostro-caudal axes which may be linked with or independent of each other. All subjects showed small but systematic increases in cycle duration over the course of individual drinking bouts. Cyclic jaw movements during drinking were correlated with nearly synchronous activity in the protractor (levator) of the upper jaw and in several jaw closer muscles, as well as with alternating activity in tongue protractor and retractor muscles. No EMG activity was ever recorded in the lower jaw opener muscle, suggesting that lower jaw opening in this preparation is produced, indirectly, by the contraction of other muscles. The results clarify the contribution of the individual jaws to the generation of gape variations during drinking in this species.Abbreviations AMEM adductor mandibulae externus muscle - DM depressor mandibulae muscle - EMG electromyographic - GENIO geniohyoideus muscle - LB lower beak - LED light-emitting diode - PQP protractor quadrati et pterygoidei muscle - PVL pterygoideus ventralis muscle, pars lateralis - SeH/StH serpihyoideus or stylohyoideus muscle - UB upper beak     

Evolutionary trend in feeding habits of <Emphasis Type="Italic">Girella</Emphasis> (Perciformes: Girellidae)

Although some Girella species are herbivorous, having basically tricuspid teeth, some are omnivorous. To determine the evolutionary trends in feeding habits of Girella, the phylogenetic relationships of several species of Girella were estimated by partially sequencing the mitochondrially encoded NADH dehydrogenase subunit 2 gene, and the dentition and adductor mandibulae complex of each species were examined. The cladogram determined from the mitochondrial DNA analysis indicated that multiple tooth-rows containing incisor-like teeth existed in adults of the ancestral species of Girella, species with a single tooth-row of tricuspid teeth in the adult stage having diverged subsequently on several occasions. The tendinous connections between each section of the adductor mandibulae complex are believed to have been simple in the ancestral species, more complicated connections also having diverged later on several occasions. Multiple tooth-rows containing incisor-like teeth and the simple adductor mandibulae complex are deduced as adaptations to herbivory; on the other hand, a single tooth-row of tricuspid teeth and the complicated adductor mandibulae complex are deduced as adaptations to omnivory. Therefore, the ancestral species of Girella is suggested as having been adapted to herbivory, with species adapted to omnivory having diverged on several subsequent occasions.     

Osteology and cranial musculature of Caiman latirostris (crocodylia: Alligatoridae)

Caiman latirostris Daudin is one of the extant species of Caimaninae alligatorids characterized taxonomically only by external morphological features. In the present contribution, we describe the cranial osteology and myology of this species and its morphological variation. Several skull dissections and comparisons with other caimans were made. Although jaw muscles of living crocodiles show the same general “Bauplan” and alligatorids seem to have a similar cranial musculature pattern, we describe some morphological variations (e.g., in C. latirostris the superficial portion of the M. adductor mandibulae externus did not reach the postorbital; the M. adductor mandibulae internus pars pterygoideus dorsalis did not reach the pterygoid and lacrimal and contrary to the case of C. crocodilus the M. adductor mandibulae internus pars pterygoideus ventralis attaches to the posterodorsal surface of the pterygoid and the pterygoid aponeurosis, without contacting the dorsal and ventral surface of the pterygoid margin; the M. intermandibularis is attached to the anterior half of the splenial and posteriorly inserts medially by a medial raphe that serves as attachment zone for M. constrictor colli, and the M. constrictor colli profundus presents a medial notch in its anterior margin). In addition, the skull of C. latirostris differs from that of other caimans and possesses several characters that are potential diagnostic features of this species (e.g., outline of glenoid cavity in dorsal view, extension of the rostral ridges, and occlusion of the first dentary tooth). Nevertheless, these characters should be analyzed within the phylogenetic context of the Caimaninae to evaluate its evolutionary implications for the history of the group. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Jaw muscle fiber type distribution in Hawaiian gobioid stream fishes: histochemical correlations with feeding ecology and behavior

Differences in fiber type distribution in the axial muscles of Hawaiian gobioid stream fishes have previously been linked to differences in locomotor performance, behavior, and diet across species. Using ATPase assays, we examined fiber types of the jaw opening sternohyoideus muscle across five species, as well as fiber types of three jaw closing muscles (adductor mandibulae A1, A2, and A3). The jaw muscles of some species of Hawaiian stream gobies contained substantial red fiber components. Some jaw muscles always had greater proportions of white muscle fibers than other jaw muscles, independent of species. In addition, comparing across species, the dietary generalists (Awaous guamensis and Stenogobius hawaiiensis) had a lower proportion of white muscle fibers in all jaw muscles than the dietary specialists (Lentipes concolor, Sicyopterus stimpsoni, and Eleotris sandwicensis). Among Hawaiian stream gobies, generalist diets may favor a wider range of muscle performance, provided by a mix of white and red muscle fibers, than is typical of dietary specialists, which may have a higher proportion of fast-twitch white fibers in jaw muscles to help meet the demands of rapid predatory strikes or feeding in fast-flowing habitats.     

An electromyographic analysis of the biting mechanism of the lemon shark,Negaprion Brevirostris: Functional and evolutionary implications

The kinetics of the head and function of select jaw muscles were studied during biting behavior in the lemon shark, Negaprion brevirostris. High speed cinematography and electromyography of seven cranial muscles were recorded during bites elicited by a probe to the oral cavity. In weak bites mandible depression was followed by mandible elevation and jaw closure without cranial elevation. In strong bites cranial elevation always preceded lower jaw depression, lower jaw elevation, and cranial depression. The average duration of the strong bites was rapid (176 msec), considering the size of the animal relative to other fishes. Different electromyographic patterns distinguished the two forms of bite, primarily in activity of the epaxial muscles, which effect cranial elevation. A composite reconstruction of the activity of seven cranial muscles during biting revealed that epaxial muscle activity and consequently cranial elevation preceded all other muscle activity. Mandible depression was primarily effected by contraction of the common coracoarcual and coracomandibularis, with assistance by the coracohyoideus. Simultaneous activity of the levator hyomandibulae is believed to increase the width of the orobranchial chamber. The adductor mandibulae dorsal was the primary jaw adductor assisted by the adductor mandibulae ventral. This biomechanically conservative mechanism for jaw opening in aquatic vertebrates is conserved, with the exception of the coracomandibularis, which is homologous to prehyoid muscles of salamanders.     

Adductor muscles of the thigh of crab-eating monkeys (Macaca fascicularis)

On the basis of 44 hindlimbs of 14 male and 14 female crab-eating monkeys (Macaca fascicularis), the morphology of the adductor muscles of the thigh was described and some functional indices were calculated. The results obtained from this study agreed generally with those of otherMacaca species reported by various authors. For the classification and nomenclature of the adductors, the criteria proposed byUhlmann (1967, 1968) was well adapted to the crab-eating monkey. The adductors comprise the m. gracilis, m. pectineus, m. adductor longus, pars longa and pars brevis of m. adductor brevis, pars lata and pars minima of m. adductor magnus and m. obturatorius externus. In males, the adductors are generally inserted further down the femur, and the insertions of pars brevis of the m. adductor brevis and pars minima of the m. adductor magnus have longer attachments to the femur than in females. The arrangement of each adductor muscle and of each fasciculus of a thigh muscle may invoke a principle of organization.     

Evolution of the feeding mechanism in primitive actionopterygian fishes: A functional anatomical analysis of Polypterus,Lepisosteus, and Amia

The comparative functional anatomy of feeding in Polypterus senegalus, Lepisosteus oculatus, and Amia calva, three primitive actinopterygian fishes, was studied by high-speed cinematography (200 frames per second) synchronized with electromyographic recordings of cranial muscle activity. Several characters of the feeding mechanism have been identified as primitive for actinopterygian fishes: (1) Mandibular depression is mediated by the sternohyoideus muscle via the hyoid apparatus and mandibulohyoid ligament. (2) The obliquus inferioris and sternohyoideus muscles exhibit synchronous activity at the onset of the expansive phase of jaw movement. (3) Activity in the adductor operculi occurs in a double burst pattern—an initial burst at the onset of the expansive phase, followed by a burst after the jaws have closed. (4) A median septum divides the sternohyoideus muscle into right and left halves which are asymmetrically active during chewing and manipulation of prey. (5) Peak hyoid depression occurs only after peak gape has been reached and the hyoid apparatus remains depressed after the jaws have closed. (6) The neurocranium is elevated by the epaxial muscles during the expansive phase. (7) The adductor mandibulae complex is divided into three major sections—an anterior (suborbital) division, a medial division, and a posterolateral division. In Polypterus, the initial strike lasts from 60 to 125 msec, and no temporal overlap in muscle activity occurs between muscles active at the onset of the expansive phase (sternohyoideus, obliquus superioris, epaxial muscles) and the jaw adductors of the compressive phase. In Lepisosteus, the strike is extremely rapid, often occuring in as little as 20 msec. All cranial muscles become active within 10 msec of each other, and there is extensive overlap in muscle activity periods. Two biomechanically independent mechanisms mediate mandibular depression in Amia, and this duality in mouth-opening couplings is a shared feature of the halecostome fishes. Mandibular depression by hyoid retraction, and intermandibular musculature, consisting of an intermandibularis posterior and interhyoideus, are hypothesized to be primitive for the Teleostomi.     

Cranial muscle development in frogs with different developmental modes: Direct development versus biphasic development

Normal development in anurans includes a free swimming larva that goes through metamorphosis to develop into the adult frog. We have investigated cranial muscle development and adult cranial muscle morphology in three different anuran species. Xenopus laevis is obligate aquatic throughout lifetime, Rana (Lithobates) pipiens has an aquatic larvae and a terrestrial adult form, and Eleutherodactylus coqui has direct developing juveniles that hatch from eggs deposited on leaves (terrestrial). The adult morphology shows hardly any differences between the investigated species. Cranial muscle development of E. coqui shows many similarities and only few differences to the development of Rana (Lithobates) and Xenopus. The differences are missing muscles of the branchial arches (which disappear during metamorphosis of biphasic anurans) and a few heterochronic changes. The development of the mandibular arch (adductor mandibulae) and hyoid arch (depressor mandibulae) muscles is similar to that observed in Xenopus and Rana (Lithobates), although the first appearance of these muscles displays a midmetamorphic pattern in E. coqui. We show that the mix of characters observed in E. coqui indicates that the larval stage is not completely lost even without a free swimming larval stage. Cryptic metamorphosis is the process in which morphological changes in the larva/embryo take place that are not as obvious as in normal metamorphosing anurans with a clear biphasic lifestyle. During cryptic metamorphosis, a normal adult frog develops, indicating that the majority of developmental mechanisms towards the functional adult cranial muscles are preserved. J. Morphol. 275:398–413, 2014. © 2013 Wiley Periodicals, Inc.     

Do constructional constraints influence cyprinid (Cyprinidae: Leuciscinae) craniofacial coevolution?

Constraints on form may determine how organisms diversify. As a result of competition for the limited space within the body, investment in adjacent structures could represent an evolutionary compromise. For example, evolutionary trade‐offs resulting from limited space in the head could have influenced how the sizes of the jaw muscle, as well as the eyes, evolved in North American cyprinid fishes. To test the evolutionary independence of the size of these structures, we measured the mass of the three major adductor mandibulae muscles and determined the eye volume in 36 cyprinid species. Using a novel phylogeny, we tested the hypotheses that the sizes of these four structures were negatively correlated with each other during cyprinid evolution. We found that evolutionary change in the adductor mandibulae muscles was generally positively and/or not correlated, suggesting that competition for space among cyprinid jaw muscles has not influenced their evolution. However, there was a negative relationship between mass of adductor mandibulae 1 and eye volume, indicating that change in these physically adjacent structures is consistent with an evolutionary constructional constraint. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 136–146.     

Ontogeny of the hyoid musculature in the African catfish, Clarias gariepinus (Burchell, 1822) (Siluroidei: Glariidae)

Three ontogenetic stages of the African catfish Clarias gariepinus have been used to describe and discuss the ontogeny of the hyoid musculature. During ontogeny, an asynchrony in the development of the muscles is observed: the intermandibularis and protractor hyoidei are the first to develop and which bear their insertions, followed by the hyohyoideus inferior and the sternohyoideus. The hyohyoideus abductor and adductor muscles are the last of the hyoid muscles to develop. In the juvenile stage (136.2 mm SL specimen), the intermandibularis is still present. The protractor hyoidei is well developed, as it may play an important role in the opening of the mouth, the elevation of the hyoid bars and, as a typical catfish feature, the displacement of the mandibular barbels. The protractor hyoidei arises as three pairs of muscle bundles (a pars ventralis, a pars lateralis and a pars dorsalis), of which the pars ventralis and the pars lateralis become fused to each other. This fusion gives rise to four different fields of superficial fibres for the manipulation of the mandibular barbels. The pars dorsalis, with its tendinous insertion, may be of more importance for mouth opening and/ or hyoid elevation. The hyohyoid muscle is well differentiated into an inferior, abductor and adductor muscles, acting on the hyoid bars, the branchiostegal rays and the opercular bone.     

Comparative anatomy of the cheek muscles within the Centromochlinae subfamily (Ostariophysi, Siluriformes, Auchenipteridae)

Glanidium melanopterum Miranda Ribeiro, a typical representative of the subfamily Centromochlinae (Siluriformes: Auchenipteridae), is herein described myologically and compared to other representative species within the group, Glanidium ribeiroi, G. leopardum, Tatia neivai, T. intermedia, T. creutzbergi, Centromochlus heckelii, and C. existimatus. The structure of seven pairs of striated cephalic muscles was compared anatomically: adductor mandibulae, levator arcus palatini, dilatator operculi, adductor arcus palatini, extensor tentaculi, retractor tentaculi, and levator operculi. We observed broad adductor mandibulae muscles in both Glanidium and Tatia, catfishes with depressed heads and smaller eyes. Similarities between muscles were observed: the presence of a large aponeurotic insertion for the levator arcus palatini muscle; an adductor arcus palatini muscle whose origin spread over the orbitosphenoid, pterosphenoid, and parasphenoid; and the extensor tentaculi muscle broadly attached to the autopalatine. There is no retractor tentaculi muscle in either the Glanidium or Tatia species. On the other hand, in Centromochlus, with forms having large eyes and the tallest head, the adductor mandibulae muscles are slim; there is a thin aponeurotic or muscular insertion for the levator arcus palatini muscle; the adductor arcus palatini muscle originates from a single osseous process, forming a keel on the parasphenoid; the extensor tentaculi muscle is loosely attached to the autopalatine, permitting exclusive rotating and sliding movements between this bone and the maxillary. The retractor tentaculi muscle is connected to the maxilla through a single tendon, so that both extensor and retractor tentaculi muscles contribute to a wide array of movements of the maxillary barbels. A discussion on the differences in autopalatine-maxillary movements among the analyzed groups is given.     

Phylogenetic relationships of the tilefish family Branchiostegidae (Pereiformes) based on comparative myology

The adductor mandibulae complex of the tilefish family Branchiostegidae contains five major subdivisions (A1α, A1β, A2, A3α and A3β). No other group of fishes among those examined exhibited the degree of complexity found among the branchiostegids. The closely related sand tilefishes (Malacanthidae) have a less complex adductor mandibulae musculature, lacking an A3β muscle. The proposed phylogeny of the branchiostegids is based upon: (1) the A3β', A3β" and A1β subdivisions, (2) overall degree of development of the adductor mandibulae (distinctness, origins, insertions, and degree of aponeurotic development). The phylogenetic implications of the adductor mandibulae complex are discussed.     

Succinic dehydrogenase activity of the respiratory muscles of a fresh-water teleost, Bagarius bagarius (Ham.) (Sisoridae, Pisces).

Functional morphology including the origin, insertion, and innervation of the respiratory muscles in relation to buccal pressure pump and opercular suction pumps in a fresh-water bottom dwelling siluroid fish, Bagarius bagarius have been studied. Histochemical studies were made on the succinic dehydrogenase activity of adductor mandibulae, retractor tentaculi, levator operculi, dilatator operculi, adductor operculi, intermandibularis, interhyoideus, hyohyoideus superior and constrictor branchialis. The intensity of reaction reveals the presence of three types of muscle fibres in some of the respiratory muscles. The muscle containing red muscle fibres are mostly innervated by the branches of the VIIth cranial nerve. The retractor tentaculi consists of superficial white muscle fibres and the interior part is dominated by red muscle fibres. The muscles (adductor operculi, levator operculi, dilatator operculi, interhyoideus, hyohyoideus superior) concerned with the opercular suction pumps are of mixed type and consist of white and red muscle fibres, whereas adductor mandibulae and intermandibularis are made up entirely of white muscle fibres. The adductor muscle bundles of the constrictor branchialis, which are responsible for movement of gill filaments, are dominated by the red muscle fibres. The abductor part, however, is made up entirely of white muscle fibres.     

Anatomy of the feeding apparatus of the lemon shark,Negaprion brevirostris

The anatomy of the feeding apparatus of the lemon shark, Negaprion brevirostris, is investigated by gross dissection, computer axial tomography, and histological staining. The muscles and ligaments of the head associated with feeding are described. The upper and lower jaws are suspended by the hyoid arch, which in turn is braced against the chondrocranium by a complex series of ligaments. In addition, various muscles and the integument contribute to the suspension and stability of the jaws. The dual jaw joint is comprised of lateral and medial quadratomandibular joints that resist lateral movement of the upper and lower jaws on one another. This is important during feeding involving vigorous head shaking. An elastic ethmoplatine ligament that unites the anterior portion of the upper jaw to the neurocranium is involved with upper jaw retraction. The quadratomandibularis muscle is divided into four divisions with a bipinnate fiber arrangement of the two large superficial divisions. This arrangement would permit a relatively greater force per unit volume and reduce muscle bulging of the jaw adductor muscle in the spatially confined cheek region. Regions of relatively diffuse integumental ligaments overlying the adductor mandibulae complex and the levator palatoquadrati muscle, interspersed with localized regions of longer tendonlike attachments between the skin and the underlying muscle, permit greater musculoskeletal movement relative to the skin. The nomenclature of the hypobranchial muscles is discussed. In this shark they are comprised of the unsegmented coracomandibularis and coracohyoideus, and the segmented coracoarcualis. © 1995 Wiley-Liss, Inc.