Homologies Of Muscles Research Articles

Homologies of the longissimus, iliocostalis, and hypaxial muscles in the anterior presacral region of extant diapsida

Homologies of muscles of the m. longissimus and m. iliocostalis groups in the dorsal and cervical regions, as well as those of the subvertebral muscles and mm. intercostales externi that continue from the dorsal into the cervical regions, in extant Diapsida are proposed based on detailed dissections and published accounts of lepidosaurs, crocodylians, and birds. The morphology of tendons and innervation patterns suggest that the avian "m. iliocostalis" in the dorsal region include the homologs of both m. longissimus and m. iliocostalis in non-avian diapsids. The conserved nature of the morphology of tendons in palaeognath birds also revealed that the avian mm. intertransversarii in the cervical region consist of muscles of the both m. longissimus and m. iliocostalis groups despite having been treated as a single series of muscles, and thus are not homologous with muscles of the same name in Lepidosauria or Crocodylia. The avian mm. inclusi that lie medial to mm. intertransversarii are homologous with mm. intercostales externi in Lepidosauria and mm. intercostales externi and m. scalenus combined in Crocodylia. Innervation patterns suggest that a muscle ("m. iliocostalis capitis") connecting the atlas rib and occiput in Crocodylia includes contributions from the subvertebral layer and m. cucullaris complex, and possibly m. iliocostalis as well. The present findings may serve as a basis for revising the currently used avian nomenclature so that it will reflect homologies of muscles with their non-avian counterparts.

Archosaur adductor chamber evolution: Integration of musculoskeletal and topological criteria in jaw muscle homology

The homologies of jaw muscles among archosaurs and other sauropsids have been unclear, confounding interpretation of adductor chamber morphology and evolution. Relevant topological patterns of muscles, nerves, and blood vessels were compared across a large sample of extant archosaurs (birds and crocodylians) and outgroups (e.g., lepidosaurs and turtles) to test the utility of positional criteria, such as the relative position of the trigeminal divisions, as predictors of jaw muscle homology. Anatomical structures were visualized using dissection, sectioning, computed tomography (CT), and vascular injection. Data gathered provide a new and robust view of jaw muscle homology and introduce the first synthesized nomenclature of sauropsid musculature using multiple lines of evidence. Despite the great divergences in cephalic morphology among birds, crocodylians, and outgroups, several key sensory nerves (e.g., n. anguli oris, n. supraorbitalis, n. caudalis) and arteries proved useful for muscle identification, and vice versa. Extant crocodylians exhibit an apomorphic neuromuscular pattern counter to the trigeminal topological paradigm: the maxillary nerve runs medial, rather than lateral to M. pseudotemporalis superficialis. Alternative hypotheses of homology necessitate less parsimonious interpretations of changes in topology. Sensory branches to the rictus, external acoustic meatus, supraorbital region, and other cephalic regions suggest conservative dermatomes among reptiles. Different avian clades exhibit shifts in some muscle positions, but maintain the plesiomorphic, diapsid soft-tissue topological pattern. Positional data suggest M. intramandibularis is merely the distal portion of M. pseudotemporalis separated by an intramuscular fibrocartilaginous sesamoid. These adductor chamber patterns indicate multiple topological criteria are necessary for interpretations of soft-tissue homology and warrant further investigation into character congruence and developmental connectivity.

Peripheral nervous system of the ocean sunfish Mola mola (Tetraodontiformes: Molidae)

Dissection of peripheral nerves in the ocean sunfish Mola mola showed the lateral line system to comprise 6 cephalic and 1 trunk lateral lines, all neuromasts being superficial. The trunk line was restricted to the anterior half of the body, the number of neuromasts (27) being fewer than those previously recorded in other tetraodontiforms. The lateral ramus of the posterior lateral line nerve did not form a “serial collector nerve” along the body. The number of foramina in the neurocranium, serving as passages for the cranial nerves, was fewer than in primitive tetraodontiforms, the reduction being related to modifications in the posterior cranium. Some muscle homologies were reinterpreted based on nerve innervation patterns. The cutaneous branch innervation pattern in the claval fin rays was clearly identical with that in the dorsal and anal fin rays, but differed significantly from that in the caudal fin rays, providing strong support for the hypothesis that the clavus comprises highly modified components of the dorsal and anal fins.

Thoracic epaxial muscles in living archosaurs and ornithopod dinosaurs

Crocodylians possess the same thoracic epaxial muscles as most other saurians, but M. transversospinalis is modified by overlying osteoderms. Compared with crocodylians, the thoracic epaxial muscles of birds are reduced in size, disrupted by the synsacrum, and often modified by intratendinous ossification and the notarium. A phylogenetic perspective is used to determine muscle homologies in living archosaurs (birds and crocodylians), evaluate how the apparent disparity evolved, and reconstruct the thoracic epaxial muscles in ornithopod dinosaurs. The avian modifications of the epaxial musculoskeletal system appear to have coevolved with the synsacrum and notarium. The lattice of ossified tendons in iguanodontoidean dinosaurs (Hadrosauridae and Iguanodontidae) is homologized to M. transversospinalis in crocodylians and M. longus colli dorsalis, pars thoracica in birds. Birds have an arrangement of tendons within M. longus colli dorsalis, pars thoracica identical to that observed in the epaxial ossified tendons of iguanodontoid dinosaurs. Moreover, many birds (such as grebes and turkeys) ossify these tendons, resulting in a two- or three-layered lattice of ossified tendons, a morphology also seen in iguanodontoid dinosaurs. Although the structure of M. transversospinalis appears indistinguishable between birds and iguanodontoid dinosaurs, intratendinous ossification within this epaxial muscle evolved convergently.

Effects of Interlimb and Intralimb Constraints on Bimanual Shoulder–Elbow and Shoulder–Wrist Coordination Patterns

The present study addressed the interactions between interlimb and intralimb constraints during the control of bimanual multi-joint movements. Participants performed eight coordination tasks involving bilateral shoulder-elbow (expt I) and shoulder-wrist (expt II) movements. Three principal findings were obtained. First, the principle of muscle homology (in-phase coordination), giving rise to mirror symmetrical movements with respect to the midsagittal plane, had a powerful influence on the quality of interlimb coordination. In both experiments, the accuracy and stability of inter- and/or intralimb coordination deteriorated as soon as the antiphase mode was introduced in one or both joint pairs. However, the mutual influences between bilateral distal and proximal joint pairs varied across coordination tasks and effectors. Second, the impact of intralimb coordination modes on the quality of intralimb coordination was inconsistent between adjacent (expt I) and non-adjacent joint (expt II) combinations. Third, the mode of interlimb coordination affected the quality of intralimb coordination, whereas strong support for the converse effect was not obtained. Taken together, these observations point to a hierarchical control structure whereby interlimb coordination constraints have a stronger impact on the global coordination of the system than intralimb constraints, whose impact is substantially dependent on effector and task. The finding that intralimb coordination is subordinate to interlimb coordination during the production of bimanual multi-joint coordination patterns indicates that symmetry is a major organizational principle in the neural control of complex movement.

Homologies of the adductor mandibulae muscles in Tetraodontiformes as indicated by nerve branching patterns

Homologies of the adductor mandibulae muscles in eight families of Tetraodontiformes were hypothesized from the branching patterns of ramus mandibularis trigeminus. Insertions of the muscles to the upper or lower jaw were weak indicators of homology, migrations of the sites occurring frequently in A1, A2α, A2β, and A3. In monacanthids, tetraodontids, and diodontids, A1 tended to be split into numerous subsections, whereas in aracanids and ostraciids, A3 was highly developed, comprising three or four subsections. In tetraodontids, A2β was found to be a composite of A1 subsection and A2β. The methods of and limits to applying nerve branching patterns to muscle homology are discussed. A new naming system that reflects both muscle homologies and insertions is proposed.

Homologies of thetransversospinalis muscles in the anterior presacral region of Sauria (crown Diapsida)

Homologies of muscles of the m. transversospinalis group in the dorsal and cervical regions in Sauria are established based on detailed dissections and published accounts of lepidosaurs, crocodylians, and birds. Attachments and directions of tendons comprising this muscle group are fairly conserved among the saurian clades, enabling rather robust inferences on muscle homologies. The innervation pattern indicates that mm. ascendentes are the most lateral muscles of the m. transversospinalis group in Aves, and are inferred to be homologous with the crocodylian m. tendinoarticularis based on their topological similarities. It is suggested here that the lepidosaurian articulo-parietalis part of m. longissimus cervico-capitis actually belongs to the m. transversospinalis group because its tendons of origin are shared with those of m. semispinalis. The avian m. complexus and the lateral part of the crocodylian m. transversospinalis capitis have origins and insertions similar to this lepidosaurian muscle, and are proposed to be homologous with the latter. In some birds, m. longus colli dorsalis, pars profunda continues directly into the anterior cervical region as m. splenius accessorius, suggesting a serially homologous relationship. Similarly, m. splenius anticus continues anteriorly from m. longus colli dorsalis, pars cranialis, and both of these muscles lie dorsal to m. splenius accessorius. Therefore, the currently used nomenclature that regards m. splenius accessorius as a part of m. longus colli dorsalis, pars cranialis and that regards m. splenius anticus as a part of the former muscle does not accurately reflect the serial homologies among these muscles and may not be justified.

Appendicular myology of the hadrosaurian dinosaur Maiasaura peeblesorum from the Late Cretaceous (Campanian) of Montana

AbstractMusculature of the pectoral and pelvic appendages and girdles of adult and nestling Maiasaura peeblesorum (Dinosauria: Ornithischia: Hadrosauridae) from the Late Cretaceous of Montana is restored according to a phylogenetically based methodology. This methodology uses an explicit, independently derived phylogenetic hypothesis of the fossil taxon and related extant taxa to generate a series of inferences regarding the presence of a muscle, its number of components, and the origin(s) and insertion(s) of these components. Corroborative osteological evidence is sought on the fossil in the form of scars and processes that fulfill the criteria for muscular attachment according to generalisations based upon extant vertebrates. A total of 46 muscles are restored, although separate attachment sites for numerous muscles cannot be discerned on the fossils. Osteological evidence for several muscles can be found in nestlings of Maiasaura despite their skeletal immaturity. Results of the phylogenetically based approach and new hypotheses for homologies of deep dorsal thigh muscles suggest that it is more parsimonious to restore the femoral insertions of M. iliofemoralis on the greater trochanter and M. puboischiofemoralis internus on the anterior (lesser) trochanter, a reversal of the traditional interpretation. The often-cited osteological specialisations of birds for flight are not accompanied in all instances by profound myological transformations, and birds must be included in any attempt to restore the myology of extinct dinosaurs.

Internuclear neurons of the ocular motor system of the larval sea lamprey.

The internuclear neurons of the ocular motor system of lampreys are characterized here for the first time. Horseradish peroxidase (HRP), fluorescein-, or Texas red-(TRDA) coupled dextran-amine applied into the oculomotor nucleus of larval lamprey (Petromyzon marinus) retrogradely labeled two populations of contralateral abducens interneurons, one lateral and the other periventricular. Tracer application to the abducens nucleus anterogradely labeled thick contralateral fibers that specifically contact the medial rectus motor subnucleus by means of large boutons. Local application of TRDA to this subnucleus allowed identification of the lateral abducens interneurons as the origin of this projection. Electron microscopy of the medial rectus motor subnucleus showed large boutons bearing round synaptic vesicles that contact on the perikarya, as well as small boutons with pleomorphic vesicles. This lateral rectus (abducens) -- medial rectus (oculomotor) internuclear projection of lampreys appears to be similar to those involved in the coordination of horizontal eye movements in mammals. The periventricular abducens interneurons projected bilaterally to other oculomotor subnuclei. Tracer application to the abducens nucleus labeled a group of small interneurons in the ipsilateral dorsal rectus motor subnucleus. Anterograde labeling indicates that oculomotor interneurons project ipsilaterally to the ventral rectus abducens subnucleus, thus, corresponding to oculomotor interneurons found in mammals and frogs. The interneurons of the dorsal rectus and ventral rectus motor subnuclei are probably involved in the control of conjugate vertical eye movements. The present results strongly suggest that the internuclear coordination of conjugate eye movements appeared in the earliest vertebrates. The homologies of extraocular muscles of lampreys and gnathostomes were reexamined.

A Model System of Structural Duplication: Homologies of Adductor Mandibulae Muscles in Tetraodontiform Fishes

We critically reviewed the homologies of the jaw muscles in tetraodontiform fishes (Triacanthoidea, Balistoidea, Tetraodontoidea), as first described in Winterbottom's phylogenetic monograph (1974, Smithson. Contrib. Zool. 155:1–201), as a case study in structural duplication. Within this order of teleost fishes, the two main adductor mandibulae muscles, A1 and A2, are duplicated one or more times in some subclades. The number of descendant A1 and A2 muscles ranges from as few as the original two muscles in triplespines to as many as eight muscles in some file-fishes. As first pointed out by Winterbottom, the homologies of some muscles are unclear, particularly in comparisons between the superfamilies Balistoidea (boxfishes, triggerfishes, filefishes) and Tetraodontoidea (pursefishes, molas, puffers, porcupinefishes). We reassessed the homologies (orthologs and paralogs) of these A1 and A2 muscles based on their origins, insertions, and relative masses in representative taxa and their congruence with a phylogeny for these taxa. New names that reflect the homologies of these muscles are presented. Ten muscle duplications by subdivision and three phylogenetic losses of muscles have occurred in this system. No relationship was found between the number of separate muscles and the relative masses of the A1 or A2 muscles, suggesting that muscle duplication events essentially repackage existing muscle tissue. However, both A1 and A2 muscle masses are correlated with each other and with the feeding ecology of these fishes. Durophagous taxa have relatively larger A1 and A2 muscles, whereas planktivores and benthic grazers have relatively smaller A2 muscles.

A Model System of Structural Duplication: Homologies of Adductor Mandibulae Muscles in Tetraodontiform Fishes

We critically reviewed the homologies of the jaw muscles in tetraodontiform fishes (Triacanthoidea, Balistoidea, Tetraodontoidea), as first described in Winterbottom's phylogenetic monograph (1974, Smithson. Contrib. Zool. 155:1–201), as a case study in structural duplication. Within this order of teleost fishes, the two main adductor mandibulae muscles, A1 and A2, are duplicated one or more times in some subclades. The number of descendant A1 and A2 muscles ranges from as few as the original two muscles in triplespines to as many as eight muscles in some file-fishes. As first pointed out by Winterbottom, the homologies of some muscles are unclear, particularly in comparisons between the superfamilies Balistoidea (boxfishes, triggerfishes, filefishes) and Tetraodontoidea (pursefishes, molas, puffers, porcupinefishes). We reassessed the homologies (orthologs and paralogs) of these A1 and A2 muscles based on their origins, insertions, and relative masses in representative taxa and their congruence with a phylogeny for these taxa. New names that reflect the homologies of these muscles are presented. Ten muscle duplications by subdivision and three phylogenetic losses of muscles have occurred in this system. No relationship was found between the number of separate muscles and the relative masses of the A1 or A2 muscles, suggesting that muscle duplication events essentially repackage existing muscle tissue. However, both A1 and A2 muscle masses are correlated with each other and with the feeding ecology of these fishes. Durophagous taxa have relatively larger A1 and A2 muscles, whereas planktivores and benthic grazers have relatively smaller A2 muscles.

Larval Shell Muscles in the Abalone Haliotis kamtschatkana.

I used light and electron microscopy to investigate shell-attached muscles in larvae of Haliotis kamtschatkana Jonas, 1845, because an early description of these muscles in H. tuberculata by Crofts (1937, 1955) has featured prominently in theories about gastropod evolution. Larval shell muscles in H. kamtschatkana can be grouped into two categories. The first category consists of the larval retractor muscle (LRM) and the accessory larval retractor muscle (ACC); these are striated muscles in which myofilaments begin differentiating before the head and foot rotate relative to the protoconch (this rotation is known as ontogenetic torsion). Collectively, these muscles ultimately insert on tissues within the larval head and mantle, but the ACC and mantle fibers of the LRM degenerate as metamorphic competence is achieved. The second category consists of two nonstriated pedal muscles that differentiate after cephalopodial rotation. The left pedal muscle is anchored on the back of the protoconch, to the left of the shell-attachment plaque for the LRM. It projects into the foot primarily, but also gives rise to muscle slips extending into the mantle fold. The right pedal muscle is anchored on a calcareous septum secreted along the visceral rim of the protoconch. The new data force a reconsideration of the ancestral homologues of larval shell muscles in abalone, because Crofts may have misidentified the accessory larval retractor muscle as a precursor of one of the later pedal muscles.

Functional Morphology of the Evolving Hand and Foot (review)

BOOK REVIEWS Functional Morphology of the Evolving Hand and Foot. By O. J. Lewis. Oxford: Clarendon Press, 1989. Pp. 359. $125. Contemporary evolutionary biologists who study the limbs of tetrapode generally do so from two perspectives. One group examines morphology for characters that may be useful in working out phylogenetic relationships. The other tries to reconstruct function for its intrinsic interest and for the insights it may yield into patterns of behavior. Of course, neither group works in isolation. A good systematist takes function into account in order to assess the phyletic stability of a character, the interrelationships of character suites, and the relative weight he may give a character on the basis of the two preceding factors. A conscientious functional morphologist looks at phylogenetic relationships because an extinct organism under study may harbor functional similarities with either related extant taxa that are experimentally accessible or better understood extinct taxa. These two perspectives have eclipsed a much older, and quite valuable, tradition of reconstructing structural/functional homologies and morphoclines. A classic example, from the axial skeleton, is the transformation of primitive synapsidjawjoint and lowerjaw into the mammalian middle ear. In this approach, strict adherence to cladistic taxonomy is not necessary to reconstruct transformation series. One needs to pay close attention to primitive versus derived character states, but these can be identified only given a broad understanding of phylogenetic relationships. In his remarkable monograph, O. J. Lewis has added a noteworthy chapter to the study ofevolutionary morphoclines. With primates as a focus, he has lovingly traced the history of the bones, ligaments, and muscles constituting the forearm, hand, leg, and foot. This is not simply a compilation of the many papers that Lewis has published over the last 3 decades; there is much new information. Moreover, the work is written as a grand synthesis, a seamless treatise in which morphology, function, and evolution are splendidly interwoven. In tracing the evolution of the distal limb segments, Lewis uses an admirably synthetic approach to determine homologies. While relying primarily on comparative anatomy, he supplements this with data from paleontology, embryology , and intraspecific variation. The last yields instructive atavisms and anticipations (as well as numerous misleading neomorphs). He shows that the most secure hypotheses are supported by congruent lines of evidence from all these data sources and recognizes the pitfalls of relying on a single body of data, citing Permission to reprint a book review printed in this section may be obtained only from the author. 152 Book Reviews several studies in which carpal and tarsal homologies were incorrecdy attributed on the basis of vague mesenchymal condensations in human embryos. Multiple criteria are used for establishing character homologies. These include topology, inter- and intraspecific morphoclines, and ontogenetic character precedence. He generally rejects the use of patterns of nerve supply to deduce the homologies of muscles, regarding these as too plastic. Lewis cautions his readers that it is necessary to establish homologies at each grade of major reorganization (e.g., rhipidistian, synapsid, cynodont, mammal, therian, placental) before moving on to the next most derived grade. Jumping directly from lobe-finned fish to human (and this has been attempted!) is fraught wtih uncertainty. In establishing character polarities (i.e., primitive vs. derived characters), Lewis again uses a range of different criteria. I support this, but Lewis is somewhat sloppy in the use of some of them. His applications ofoutgroup analysis are not rigorous and are sometimes downright arbitrary. To reconstruct the primitive morphotype for the synapsid ancestors of mammals, he often relies only on the rhyncocephalian Sphenodon. For the forelimb especially, he usually chooses only few representative marsupials and placentals that appear to him to be primitive, and then pronounces the skeletomuscular morphology primitive on that intuitive basis alone. Moreover, different taxa are often used to establish the primitive morphotype for each anatomical unit, producing a lack ofcomparability between units. Within primates, he implicitly places great weight on the somewhat hazardous criterion of in-group comparisons—in other words, trusting that the wider a trait is distributed, the more likely it is to be primitive. To root his morphoclines (i.e., to establish their direction), Lewis often uses an unstated weighting system based on the likelihood...

Lumbrical function: Interaction of lumbrical contraction with the elasticity of the extrinsic finger muscles and its effect on metacarpophalangeal equilibrium

Since conflicting statements have been made in the literature regarding the influence of lumbrical contraction on the metacarpophalangeal (MP) joint, a study was undertaken to determine the length-tension curve for the index flexor profundus. Four fresh cadaver hands were used. Measurements for the flexor superficialis and for the common extensor were determined in there. The measurements were correlated with measured displacement of these tendons in six finger positions. Isolated lumbrical contraction was then mechanically simulated, acting against spring homologues of the index extrinsic muscles. The finger moved from the rest position toward the intrinsic position with loads of less than 5 N. This demonstrated that in addition to its effect on interphalangeal joint extension, the lumbrical acting alone can cause flexion of the metacarpophalangeal joint.

The localization of motoneurons supplying the hindlimb muscles of the mouse.

The method of retrograde axonal transport of horseradish peroxidase (HRP) has been used to localize the motoneurons that innervate the mouse hindlimb musculature. Motoneurons were labelled following either intramuscular injection of an HRP solution or application of HRP to the cut end of a muscle nerve. When intramuscular injection was used the nerves to adjacent muscles were cut and deflected from the injection site to prevent motoneurons projecting to these muscles being labelled with HRP. For some muscles this procedure was inadequate since the nerves to adjacent muscles were too short to enable adequate deflexion. The motoneurons projecting to these muscles were labelled by the method of cut nerve exposure. The motoneurons that project to a single muscle or a group of muscles were organized as longitudinal columns. The positions of such motonuclei within the lateral motor column were similar in different animals for any given muscle or muscle group. Motoneurons innervating the anterior and medial femoral muscles were located in spinal segments L1 and L2. Motoneurons innervating the remaining hindlimb muscles were found in segments L3-L5. Topographic relationships between muscle motonuclei were in general found to be similar to those described for the cat. The principal differences to be noted between the two species were that the adductors motonucleus did not overlap with the hamstrings motonucleus in the mouse. Also the motonuclei supplying the deep flexors of the crural musculature and intrinsic musculature of the foot were located more ventrally relative to the posterior crural motonucleus in the mouse as compared to the cat. Consideration of muscle homologies between vertebrate classes enabled comparisons of the localization of motonuclei between the mouse and the other species studied. It was found that topographical relations between motonuclei were similar in all the species so far studied. There was no absolute correlation between the rostrocaudal position of a motonucleus and the position in the hindlimb of the muscle that it innervated. In general, motonuclei innervating muscles derived from the dorsal muscle mass were located lateral to motonuclei innervating muscles derived from the ventral muscle mass. Furthermore, within each muscle mass there is a relationship between rostrocaudal position of a motonucleus and the anteroposterior position of the muscle it supplies. Thus there is a relation between position of a motonucleus within the spinal cord and the derivation from the embryonic muscle mass of the muscle that it supplies.

Phenetic analysis of the stomatogastric musculature of several decapod Crustacea

If the evolution of the decapod Crustacea is, to a large extent, the evolution of their feeding methods, then evolutionary relationships should be reflected in the skeletal, muscular, and neural organization of the stomatogastric system. Homologies of the stomach muscles of several species of decapod Crustacea were identified by ossicle attachment sites. All species within a single infraorder were highly similar in muscle organization to each other but clear differences between infraorders were noted. A phenetic analysis yields a phenogram which reproduces the taxonomic scheme of earlier zoologists, based on independent external morphological characters. Identification of muscle relationships in this way is an essential step towards the comparative study of small motor systems producing stereotyped behaviors.

Comparative study of the stomatogastric system of the decapod crustacea. II. Musculature.

The stomach musculature of several species of decapod Crustacea is described in detail. All species are sufficiently similar so that muscle homologies can be established. The Natantia have a simplified muscle system while the Reptantia are characterized by a more complex muscle system. Species can be arranged in a graded series of muscle system complexity which closely follows the evolution of the decapod Crustacea. The information presented here should provide the basis for consistent identification of the stomatogastric motor neurons throughout the decapod Crustacea.

On the rami intermedii of the spinal nerves and their equivalent offshoots. A contribution to classification of the trunk muscles.

Distribution patterns of the nerves of supply to the intertransversarii posteriores cervicis, levatores costarum breves and intertransversarii laterales lumborum were carefully studied in nine body-halves of male human cadavers. Any of these muscles lie wegded in between the commencements of the dorsal and ventral primary rami of the spinal nerves. In the great majority of the cases the levatores costarum breves derived their nerve supply in the upper segments from both primary rami of the corresponding spinal nerves and in the lowest segments as the rami intermedii from the bifurcation of each spinal nerve into its primary rami. Both patterns of the nerve supply to the levatores costarum breves were turned into one another in the intervening segments. The intertransversarii posteriores cervicis of similar location to the levatores costarum breves in the thoracic region were regarded as the upper serial homologues of these muscles, because they were supplied by both primary rami of the spinal nerves, similarly the intertransversarii laterales lumborum, principally supplied by the rami intermedii of the spinal nerves, as the lower serial homologues of the same muscles.

The Musculature of the Head Appendages and the Cephalic Stomodaeum of Pieris brassicae (Lepidoptera: Pieridae)1

Part I of this study describes the muscles of the antennae, labrum, mandibles, maxillae, labium, the cibariobuccal region, pharynx, and esophagus of the caterpillar. The first, second, and fourth dorsal dilators of the pharynx arise on the clypeus and the epistomal ridge rather than on the frontal region; this is correlated with a narrowing of the frons. The difficulties inherent in attempts to establish muscle homologies solely on the basis of their attachments are made apparent. Part II describes these muscles in the adult butterfly. The cibarial and buccopharyngeal region contribute to the sucking pump, whose major portion is formed by the cibarium. The hypopharynx is extended more anteroposteriorly in the adult than in the larva, giving the erroneous impression that, relative to the parts concerned, the frontal ganglion has moved backwards.

Studies on the Hexapod Nervous System. I. The Peripheral Distribution of the Thoracic Nerves of the Adult Cockroach, Periplaneta Americana1

Eight pairs of nerves emanate from each of the three thoracic ganglia of the adult American cockroach. An additional chiasmic nerve, probably proprioceptive in function, is present in the pro thorax. The interganglionic connective is designated as nerve 1. Nerve 2A supplies the intersegmental muscles and others which, collectively, probably play an important role in the maintenance of posture. Nerve 2B of the meso- and metathorax is primarily sensory to the spiracular region, tegula, wings, and axillary region. Nerve 2C supplies the dorsal longitudinal and oblique muscles. Nerve 3A supplies coxal adductors and promotors, while 3B comprises the major sensory supply of the coxa. Nerve 4 supplies the main depressor of the leg, certain coxal remotors, and muscles which probably act as adductors and rotators. In the coxa nerve 5 is sensory to the coxal wall and meron, motor to the coxal branches of the main leg depressor. Nerve 6A supplies the coxal remotors; 6B the major levators of the leg, as well as muscles which probably function as coxal rotators or rotator-adductors. Nerve 7 provides the sensory supply of the basisternal and furcasternal setae. Nerve 8 supplies the spiracular closing muscle. The metathoracic and first abdominal ganglia are fused. The two nerves emanating from the first abdominal ganglion are characterized. Difficulties likely to be encountered in using nerve distribution to establish muscle homologies are discussed.