THE ONTOGENY OF THE CRANIAL BONES, CRANIAL PERIPHERAL AND CRANIAL PARASYMPATHETIC NERVES, TOGETHER WITH A STUDY OF THE VISCERAL MUSCLES OF STRUTHIO

Abstract The skull of Struthio is typically avian. There are, however, many cranial features that are neotenic in relation to the other Dromaeognathae and Neognathae. The premaxillary-vomer arthrosis is present in the embryo of Struthio but is absent in the adult; it is present in the adults of the other Dromaeognathae; the trabeculo-capsular entity is uninterrupted: therefore, there is no mesokinetic joint; kinesis, as a result, is limited. No orbitosphenoid present; septum ossifies as mesethmoid which appears on the dorsal surface. There are only two circumorbital bones present: the lacrimal and the jugal. The auditory region has only two centres of ossification: the prootic and opisthotic. The quadrate has a single elongated condyle of the processus oticus which articulates with the prootic and squamosal. The cranial base is ossified as the basioccipital and basisphenoid, the latter being of mixed origin. There are five dermal bones in the lower jaw of Struthio ; the gonial is present. The trigeminus musculature is reduced and shows very definite neotenic features. The peripheral cranial nerves are typically avian. The cranial parasympathetic nerves are well developed in the embryo but show definite signs of resorption in the later stages of development. The hyoid apparatus is mainly cartilaginous; the hyoid musculature is reduced.     

Cephalic anatomy of the rare Indonesian snake Anomochilus weberi

The head of Anomochilus weberi combines features seen in living uropeltines and scolecophidians, two clades of fossorial snakes that appear to have the most specialized and, at the same time, the most divergent modifications of the head. However, the weakly supported premaxilla of Anomochilus departs from both scolecophidian and uropeltine modes of reinforcing the anterior tip of the snout, suggesting that Anomochilus is a less specialized burrower. Its skull also has a number of features unusual among snakes, including a unique buttress on the anterior ends of the septomaxillae, an ectopterygoid reduced to a splint that touches neither maxilla nor pterygoid, a short maxillary tooth row oriented at 45° to the long axis of the skull, and a braincase and snout complex that are uniformly wide. The features of the upper jaw are predicted to confer behavioural and mechanical attributes intermediate between those of typhlopid scolecophidians and uropeltines.     

Skeletal development of the direct-developing caecilian <Emphasis Type="Italic">Gegeneophis ramaswamii</Emphasis> (Amphibia: Gymnophiona: Caeciliidae)

A few previous studies of skeletal and especially skull development in Gymnophiona often provided contradictory results. We studied the development of the skull and vertebral column of Gegeneophis ramaswamii, a direct-developing Indian caeciliid, based on 13 specimens. The chondrocranium forms at (Brauer in Zool Jahrb Anat 12:477-508,1899) stage 38. First dermal and perichondral ossifications occur at stage 40. The first dermal bones to form are the mentomeckelian, dentary, angular, vomer, and premaxillary. These are followed by the coronoid, palatine, pterygoid, maxillary, and the skull-roofing bones. The last occurring dermal ossifications are the parasphenoid and the squamosal. We present evidence for the occurrence of a lacrimal bone. No ectopterygoid, basioccipital, supraoccipital, pleurosphenoid, postorbital, or supratemporal elements were found. We assess the homology of the bones constituting the caecilian skull and discuss the above-mentioned terminologies. The phylogenetic implications of our findings are briefly discussed and we conclude that the evidence from developmental morphology is at present consistent with a monophyletic Lissamphibia of temnospondyl origin.     

Early development of the cephalic skeleton of Barbus barbus (Teleostei, Cyprinidae)

The inception, and development of the cephalic skeleton of Barbus barbus from hatching to 24 days passes through periods of fast and slow growth; these rates are not the same in different parts of the skull. Trabeculae, parachordal plates, Meckelian cartilages and hyposymplectics are present at hatching. Then the cartilaginous floor of the neurocranium develops, the pars quadrata, the hyoid bars and branchial arches elements appear shortly before the first movable dermal bones, the dentaries, maxillae and opercles. The first bone of the braincase to appear is the parasphenoid; other bones develop subsequently and at the same time: the angular, quadrate, interopercle and fifth ceratobranchial. Later the splanchnocranium continues to develop at a relatively fast rate while the neurocranium shows little growth. The braincase does not begin to close before the 24th day, nor do the first bones of the skull roof appear, while the bucco-pharyngeal apparatus is complete, having the adult shape. The early constitution of the latter structures seems to be linked with the mechanical demands of biological functions such as breathing and feeding.     

Sequence of ossification in the skeleton of growing and metamorphosing tadpoles of Rana pipiens

The order of ossification of bones in the skeleton of Rana pipiens during larval growth and metamorphosis has been determined from observations on specimens fixed in 70% alcohol and stained with alizarin red S. The axial skeleton ossifies in a generally cephalo-caudal sequence, beginning with the parasphenoid bone at Taylor-Kollros stages IV-IX, followed by vertebrae (V-IX) and then the urostyle (IX-XIV). Exoccipitals (VII-IX), frontoparietals (XI-XII) and prootics (XIII-XVII) are additional cranial bones which successively ossify before metamorphosis. With the onset of metamorphosis at stage XVIII jawbones and rostral bones of the skull ossify in the following succession: premaxilla, maxilla, septomaxilla, nasal, dentary, angular, squamosal, pterygoid, prevomer, mentomeckelian, quadratojugal, palatine, columella, posteromedial process of “hyoid.” The sphenethmoid does not ossify until after metamorphosis. Ossification of limbbones begins with the femur or humerus at stages X-XII and progresses proximo-distally to the phalanges by stages XIII-XV. Carpals, however, do not ossify until stage XXV or after metamorphosis. The ilium of the pelvic girdle begins to ossify at stages X-XII, but the ischium is delayed until stages XX-XXIII. Scapula and coracoid of the pectoral girdle undergo initial ossification at stages XII-XIV, suprascapula and clavicle at stages XIII-XV. The sternum does not begin to ossify until stage XXIV. The possible role of thyroid hormones in stimulating osteogenesis is discussed.     

三列齿类爬行动物化石在新疆的发现

本文报道的三列齿类化石是该类动物在我国西北地区之首次出现,与四川自贡所产大山铺恐龙动物群中的自贡似卞氏兽(Bienotheroides zigongensis)归同属同种,故认为五彩湾组可与下沙溪庙组相对比。新标本的发现在若干形态特征上补充了以往记述之不足。     

Cranial anatomy of the extinct amphisbaenian Rhineura hatcherii (Squamata, Amphisbaenia) based on high-resolution X-ray computed tomography

The fossilized skull of a small extinct amphisbaenian referable to Rhineura hatcherii Baur is described from high-resolution X-ray computed tomographic (HRXCT) imagery of a well-preserved mature specimen from the Brule Formation of Badlands National Park, South Dakota. Marked density contrast between bones and surrounding matrix and at bone-to-bone sutures enabled the digital disarticulation of individual skull elements. These novel visualizations provide insight into the otherwise inaccessible three-dimensionally complex structure of the bones of the skull and their relationships to one another, and to the internal cavities and passageways that they enclose. This study corrects several previous misidentifications of elements in the rhineurid skull and sheds light on skull construction generally in "shovel-headed" amphisbaenians. The orbitosphenoids in R. hatcherii are paired and entirely enclosed within the braincase by the frontals; this is in contrast to the condition in many extant amphisbaenians, in which a large azygous orbitosphenoid occupies a topologically distinct area of the skull, closing the anterolateral braincase wall. Rhineura hatcherii retains a vestigial jugal and a partially fused squamosal, both of which are absent in many extant species. Sculpturing on the snout of R. hatcherii represents perforating canals conveying sensory innervation; thus, the face of R. hatcherii receives cutaneous innervation to an unprecedented degree. The HRXCT data (available at www.digimorph.org) corroborate and extend previous hypotheses that the mechanical organization of the head in Rhineura is organized to a large degree around its burrowing lifestyle.     

The impact of metamorphosis on the cranial osteology of giant salamanders of the genus Dicamptodon

Pacific giant salamanders (Dicamptodon) rank among the largest terrestrial caudates. Their ontogeny produces two distinct morphs—larval‐neotenic and metamorphosed—which differ in many morphological traits. We identified changes that are initiated by metamorphosis (distinguishing transformed from neotenic specimens) and also recognized age‐related changes occurring irrespective of transformation. During metamorphosis, specimens remodel the palate, rearrange the vomerine dentition, expand the maxilla, broaden the cheek, foreshorten the posterior skull table and develop specific serrated suture patterns in the dermal bones. Instead, large larvae grow a robust pterygoid sutured with a fully ossified trapezoidal vomer and a short maxilla. Small larvae are readily distinguished by tooth count, morphology and arrangement from more advanced larvae. Age‐related features, irrespective of metamorphosis, include pedicellate teeth, morphological differentiation of parasphenoid, enlargement of the orbitosphenoid, distal expansion of columella, and loss of coronoid teeth.     

Latimeria chalumnae and its pedigree

Synopsis Latimeria is the product of a long coelacanth lineage, usually viewed as having changed very little. In this paper a classification of better known coelacanth genera is proposed based on a cladistic computer analysis of 56 morphological characters. Biometrical data are then matched with the classification to explore the possibility of identifying subtle change. It is concluded that throughout coelacanth history there have been changes in the structure of the vertebral column involving an overall increase in the number of vertebral elements, and a consequent crowding of these elements within the abdominal region. These changes may be associated with increasing lobation of the second dorsal and anal fins. In the skull, parameters involving the intracranial joint have also changed in such a way that the anterior part of the skull has lengthened in relation to the posterior part and this may be associated with an increase in length of the basicranial muscle.Abbreviations in text figures Ang angular - a.o.r anterior opening of th rostral organ - Art articular - ba.cr.m basicranial muscle - Basi basisphenoid - Boc basioccipital - bpt.pr basipterygoid process - c.p.l cheek pit line - De dentary - Esc extrascapular - eth.sp etmosphenoid - f.e frontoethmoid - Fr frontal - Fr.d descending process of frontal - intr. j intracranial joint - io.s interorbital septum - sc jugal sensory canal - L.e lateral ethmoid - m.Cor modified coronoid - Mm memtomeckelian - m.ot.sc medial branch of otic canal - Op operculum - o.p.l oral pit line - ot,occ otico-occipital - Pa parietal - Pa.d descending process of parietal - Par parasphenoid - pa.s parietal shield - p.Cor principal coronoid - Po postorbital - Pop preoperculum - p.o.r posterior openings of the rostral organ - Pmx premaxilla, Pre-preorbital - Pro prootic - Pro.p posterior process of prootic - Rart retroarticular - Sc.o sclerotic ossicle - So supraorbital - Soc supraoccipital - Sop suboperculum - Sp spiracular - spl splenial - Sq squamosal - Stt supratemporal - Stt.com supratemporal commissure - Stt.d descending process of supratemporal - Par.a.w ascending wing of parasphenoid - Te tectal - X level of vagus exit     

早白垩世热河生物群一新的有尾两栖类

描述了内蒙古宁城下白垩统义县组下部一新的有尾两栖类：奇异热河螈（新属、新种）Ｊｅｈｏｌｏｔｒｉｔｏｎ ｐａｒａｄｏｘｕｓ ｇｅｎ． ｅｔ ｓｐ． ｎｏｖ．。标本保存了完好的相关节的骨架印痕,头骨中的翼 骨具有一个不与上颌骨相连,而与头骨中部相连的前内侧突,这使它区别于其他早期有尾类。     

陕北槽齿类新发现

本文记述了采自陕北府谷县三迭系和尚沟组上部的一槽齿类化石。根据骨髂形态特征认为属于古鳄亚目的原鳄科,与Chasmatosaurus和Elaphrosuchus相近,但上颌骨参与外鼻孔的构成及前上颌骨不呈喙嘴状等却显著不同。为此另建立一新属(Xilousuchus)。考虑其一些进步的构造、新属种的生存时代应稍晚于上述Chasmatosaurus和Elaphrosuchus。     

Architecture of the masticatory apparatus in eastern raccoons (Procyon lotor lotor)

The structure and function of the masticatory apparatus of raccoons resemble those found in carnivores. In this study, the architecture of the skull, dentition, and masticatory apparatus is described, and a model is proposed that suggests a mechanism used by raccoons to reduce different foods. The model suggests that jaw movements are similar to those of cats, the posterior regions of the superficial and deep parts of the temporalis and the anterior region of the medial pterygoid generate horizontal jaw movements, and the anterior portions of the superficial and deep temporalis as well as portions of the masseteric complex generate vertical closing movement. The distributions of slow, fast fatigable, and fast fatigue-resistant fibers for the temporalis and masseteric complex are related to the possible actions of these muscles during mastication, as are the regional cross-sectional areas of the masticatory muscles.     

Feeding mechanism of Epibulus insidiator (Labridae; Teleostei): Evolution of a novel functional system

The feeding mechanism of Epibulus insidiator is unique among fishes, exhibiting the highest degree of jaw protrusion ever described (65% of head length). The functional morphology of the jaw mechanism in Epibulus is analyzed as a case study in the evolution of novel functional systems. The feeding mechanism appears to be driven by unspecialized muscle activity patterns and input forces, that combine with drastically changed bone and ligament morphology to produce extreme jaw protrusion. The primary derived osteological features are the form of the quadrate, interopercle, and elongate premaxilla and lower jaw. Epibulus has a unique vomero-interopercular ligament and enlarged interoperculo-mandibular and premaxilla-maxilla ligaments. The structures of the opercle, maxilla, and much of the neurocranium retain a primitive labrid condition. Many cranial muscles in Epibulus also retain a primitive structural condition, including the levator operculi, expaxialis, sternohyoideus, and adductor mandibulae. The generalized perciform suction feeding pattern of simultaneous peak cranial elevation, gape, and jaw protrusion followed by hyoid depression is retained in Epibulus. Electromyography and high-speed cinematography indicate that patterns of muscle activity during feeding and the kinematic movements of opercular rotation and cranial elevation produce a primitive pattern of force and motion input. Extreme jaw protrusion is produced from this primitive input pattern by several derived kinematic patterns of modified bones and ligaments. The interopercle, quadrate, and maxilla rotate through angles of about 100 degrees, pushing the lower jaw into a protruded position. Analysis of primitive and derived characters at multiple levels of structural and functional organization allows conclusions about the level of design at which change has occurred to produce functional novelties.     

Jaw muscles and the skull in mammals: the biomechanics of mastication.

Among non-mammalian vertebrates, rigid skulls with tight sutural junctions are associated with high levels of cranial loading. The rigid skulls of mammals presumably act to resist the stresses of mastication. The pig, Sus scrofa, is a generalized ungulate with a diet rich in resistant foods. This report synthesizes previous work using strain gages bonded to the bones and sutures of the braincase, zygomatic arch, jaw joint, and mandible with new studies on the maxilla. Strains were recorded during unrestrained mastication and/or in anesthetized pigs during muscle stimulation. Bone strains were 100-1000 micro epsilon, except in the braincase, but sutural strains were higher, regardless of region. Strain regimes were specific to different regions, indicating that theoretical treatment of the skull as a unitary structure is probably incorrect. Muscle contraction, especially the masseter, caused strain patterns by four mechanisms: (1) direct loading of muscle attachment areas; (2) a compressive reaction force at the jaw joint; (3) bite force loading on the snout and mandible; and (4) movement causing new points of contact between mandible and cranium. Some expected patterns of loading were not seen. Most notably, strains did not differ for right and left chewing, perhaps because pigs have bilateral occlusion and masseter activity.     

记裂头鳄属(Dibothrosuchus)一新种

本文记述的裂头鳄属-新种 (Dibothrosuchus xingsuensis sp. nov.)的标本采自云南禄丰盆地下禄丰组深红层.通过描述,对裂头鳄属属级特征作了补充.新种的头骨中鳞骨缺失降突;方骨极度向前背方伸展,形成大的耳凹,乌喙骨具后腹突,以及具有鳄类式的腕骨等,表明裂头鳄属应改属为楔形鳄科 (Sphenosuchidae).根据该科各属的头骨中方骨与脑颅侧壁的连接关系,可以清楚地看到楔形鳄科在这局部解剖学上存在一连续的发展过程.在形态上,裂头鳄属和南非的 Sphenosuehus (典型属)最为相近.     

Cranial and appendicular ontogeny of Bactrosaurus johnsoni,a hadrosauroid dinosaur from the Late Cretaceous of northern China

Abstract: The juvenile anatomy of various cranial and appendicular elements of the hadrosauroid dinosaur Bactrosaurus johnsoni is described in detail. Growth changes are documented from juvenile to adult stages for each skeletal element available. In the studied skull, ontogenetic trends consist of: development of features on the ventral surface of the frontal; reduction in the slope of the posteromedial process of the premaxilla; a posterior shift of the dorsal process of the maxilla; development of concavities on the medial surface of the prefrontal; increased robustness and development of the ventral flange of the jugal; decreased curvature of the long axis of the quadrate; increased ventral deflection of the dentary; and changes in the length/width proportions and depth of the anterior surface of the predentary. In the appendicular skeleton, the majority of ontogenetic variation from juvenile to adult occurs in the limb bones, including increased robustness of the deltopectoral crest of the humerus; relative shortening of the ulna; increased development of the fourth trochanter and mediolateral widening of the distal end of the femur; increased expansion of the cnemial crest of the tibia; and the increased prominence of articular protuberances and flanges of the metatarsals. A survey of the phylogenetically informative characters present in B. johnsoni indicates that several characters concerning the frontal, maxilla, jugal, quadrate, predentary, dentary, scapula, humerus and ilium are affected by ontogeny. Nevertheless, the majority of phylogenetic characters are not ontogenetically variable, suggesting that a substantial amount of the information provided by juvenile and subadult specimens for phylogenetic inference is reliable in basal hadrosauroids.     

Early development of the cephalic skeleton in the turbot

At hatching Scophthalmus maximus shows no cartilaginous and no bony structure. Mecke?s cartilages appear when the fry are 1 day old, followed on day 2, by formation of the trabecular bars, fused at the outset to form a trabecula communis. Concurrently, the palatoquadrates complete the mandibular arch, and the first two pairs of ceratobranchials, associated with a pair of hyoid bars, form the beginnings of the hyobranchial system. By day 3, the parachordals have fused with the trabecular bars, the hyosymplectics have linked to the hyoid bars by interhyals, and the first four pairs of ceratobranchials have appeared. The first bony structures appear: the preoperculars. On day 8, the frontals develop above the orbits and the maxillaries and dentaries appear. On day 10, the primordia of the taeniae marginales appear, the palatoquadrates bear a pterygoid process, and to the branchial basket have been added the fifth pair of ceratobranchials and the four pairs of epibranchials. On day 12, both pairs of posterior pharyngobranchials are present. The premaxillaries develop in front of the maxillaires, and retroarticulars and the angulars complete the lower jaws. On day 13, a thin parasphenoid contributes to the floor of the neurocranium, and ectopterygoids and entopterygoids to the splanchnocranium. The set of opercular bones is complete. On day 15, the tectum synoticum closes the braincase posteriorly. The splanchnocranium possesses a basihyal and the pharyngobranchials of the first epibranchials. On day 18, the tectum posterius completes the dome of the braincase. The rear end and lateral walls of the skull are formed by the basioccipital, the exoccipitals, the pterotics, and the parietals. The suspensorium is nearly complete. From day 10, the first resorptions begin in parallel with the construction of the chondrocranium. Mecke?s cartilages each split in two, then the posterior part of the trabecular bars disappears. On day 23, the right taenia marginalis separates from the lamina orbitonasalis and curves towards the centre. Simultaneously, the right eye begins its migration to the left. This is the only metamorphosis-linked asymmetry to appear during the development of the chondrocranium. On day 25, many more bony structures appear, a characteristic of this stage: the nasals, lateral ethmoids, mesethmoid, sphenotics, prootics, pleurosphenoids, epiotics, and supraoccipital. From this stage on, the bony structures continue to develop, while the front of the neurocranium and the jaws undergo a deep remodelling due to metamorphosis. The left taenia marginalis does not appear reduced until day 29. By day 45, there remain only a few small elements of the cartilaginous skull.