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Tzetlin, A. B. 222_. Ultrastructural study of the jaw structures in two species of Ampharetidae (Annelida: Polychaeta).— Acta Zoologica(Stockholm)85: 171–180Two species of jaw bearing Ampharetidae (Adercodon pleijeli(Mackie 1994) andAmpharetesp. B) were investigated in order to describe the microanatomy of the mouth parts and especially jaws of these enigmatic polychaetes. The animals of both studied species have 14–18 mouth tentacles that are about 30 µm in diameter each. In both species, the ventral pharyngeal organ is well developed and situated on the ventral side of the buccal cavity. It is composed of a ventral muscle bulb and investing muscles. The bulb consists of posterior and anterior parts separated by a deep median transversal groove. In both species, the triangular teeth or denticles are arranged in a single transversal row on the surface of the posterior part of the ventral bulb just in front of its posterior edge. There are 36 denticles inAdercodon pleijeliand 50 inAmpharetesp. B. The height of the denticles (6–12 µm) is similar in both species. Each tooth is composed of two main layers. The outer one (dental) is the electron-dense sclerotized layer that covers the tooth. The inner one consists of long microvilli with a collagen matrix between them. The thickness of the dental layer ranges from 0.95 to 0.6 µm. The jaws of the studied worms may play a certain role in scraping off microfouling. The fine structure of the jaws in Ampharetidae is very similar to that of the mandibles of Dorvilleidae, the mandibles and the maxillae of Lumbrineridae, Eunicidae and Onuphidae, and the jaws of other Aciculata. This type of jaw is characterized by unlimited growth and the absence of replacement. The occurrence of jaws in a few smaller Ampharetidae is considered as an apomorphic state. [ABSTRACT FROM AUTHOR]

In cetaceans, each otic capsule is bound anteriorly to the remainder of the endocranium by an aliform structure called the supracochlear lamina. This lamina has been established here as the homologue of the sphenocochlear commissure of other mammals. Most researchers believe that these two structures arose within mammals. However, a comparative study involving data from both extant and extinct craniates suggests that the supracochlear lamina and the sphenocochlear commissure have a long premammalian history. The conclusion is that the lower of the two pharyngeal segments at the upper end of the mandibular branchial arch first became incorporated in the endocranium, constituting the cartilago trabecularis in the embryos of jawed craniates. The distal, or posterior, extremity of the trabecular cartilage projected outwardly to form the basitrabecular process. This process, which when ossified is called the processus basipterygoideus, functioned as a jaw support. Later, one more jaw support, termed the basivincular. evolved immediately in front of the basipterygoid process. Both these supports for the upper jaw existed in the piscine forerunners of the tetrapods. Subsequently, in the lineages leading to mammals, the basivincular jaw support became the processus alaris to which is attached an upper jaw endoskeletal remnant, called the ala temporalis. The basipterygoid jaw support, however, vanished as a consequence of the evolution of an exoskeletal joint system for the jaws of mammals. Yet the basipterygoid process persisted and as the sphenocochlear commissure or the supracochlear lamina assumed the new function of supporting the cochlear part of the auditory capsule. [ABSTRACT FROM AUTHOR]

The issue of the origin and phylogenetic significance of the ‘intracranial joint’ and the ‘ventral otic fissure’ has in recent years been much debated. Two antipodal opinions exist. One calls for their origin independently of one another and maintains that they represent relatively primitive features. The other holds them to be specializations derived from an erstwhile basicranial fissure which either became extended up to the roof of the cranium or, from a position close behind the hypophyseal fossa, migrated backwards, as the posterior myodome developed. In this paper, the former view is upheld, whereas the latter is demolished. [ABSTRACT FROM AUTHOR]

The distal part of the filum terminale is continuously reduced during the postnatal development in young rats. Simultaneously with the reduction the ampulla terminalis is placed in cranial direction. In this ampulla the fiber of Reissner is broken down. After transsection of the filum removing of the fiber takes place in the distal part. The disappearence of fiber did not effect the normal tail growth in young rats. [ABSTRACT FROM AUTHOR]

In hynobiid urodele embryos there are three serially arranged muscles associated with the otic and occipital regions of the endocranium. These muscles are continuous posteriorly with the succession of trunk myomeres and most likely represent myotomic derivatives attributable to the third, fourth, and fifth metameres of the body. From front to back these muscles are designated: anterior basiotic, posterior basiotic, and occipital. A hitherto unknown cranial nerve is directed towards the posterior basiotic muscle in embryos of Hynobius retardatus. For this new somatic motor nerve the term nervus tenuis is proposed. Together with the glossopharyngeal nerve it constitutes the fourth cranionerval segment. [ABSTRACT FROM AUTHOR]

The anatomy of the head is described for three species of syrphid larvae of differing feeding habits and the relation of the structure to the function is shown. The degree of adaptation of both the musculature and the skeletal parts of the cephalopharynx to the type of food which the larva partakes is discussed. The mouthparts are discussed in detail and the probable course by which the complex mandibular lobes of aquatic, filter-feeding syrphid larvae were evolved, is pointed out. [ABSTRACT FROM AUTHOR]

In the present paper, the otic capsule, palate, temporal bones, lower jaw and hyoid apparatus of the skull of the adult Egyption cobra, Naja haje, have been described in detail, and compared with those of the previously studied ophidian species. The otic capsule is composed of the prootic, laterosphenoid and opisthotic. The fenestra ovalis interrupts the suture separating the prootic and the opisthotic part of the otoccipital. The laterosphenoid is a rather minute bone lying lateral to the center of the prootic, with which it is completely fused both above and below without any trace of sutures. The palate is composed of the premaxillae, maxillae, prevomers, septomaxillae, palatines, pterygoids, ectopterygoids, basisphenoid and parasphenoid. There is no actual contact between the two prevomers. Each prevomer is composed of a median vertical part and a lateral horizontal one. It is quite separate from the premaxillae, maxilla and palatine. The septomaxilla is wedged between the nasal dorsally, the premaxilla anteroventrally, and the prevomer postero-ventrally. The palatine is connected posteriorly with the pterygoid and laterally (by means of an outer process) with the palatal process of the maxilla. It carries about seven teeth. The pterygoid is a very long bone, it is connected with the quadrate only by a ligament. The pterygoid is free from the brain-case, and carries about fourteen teeth. The ectopterygoid connects the maxilla with the pterygoid. The epipterygoid is completely absent. The basisphenoid is completely fused anteriorly with the parasphenoid without any trace of a suture. The parasphenoid is firmly fixed above to the lateral downgrowths of the frontals, and suturally articulates postero-laterally with the lateral downgrowths of the parietals. There is only one temporal bone on either side which is regarded as the supratemporal. Thus the squamosal and tabular are completely absent. This supratemporal holds the quadrate to the cranium. Each mandibular ramus is composed of four distinct bones which are the dentary, splenial, angular and a composite bone. This composite bone is the result of the complete fusion of the articular, prearticular and supra-angular. The coronoid bone is completely lacking. The cartilaginous hyoid apparatus is composed of two very long ceratohyals which are fused anteriorly to a small hyoid corpus. [ABSTRACT FROM AUTHOR]

In the present article, the median dorsal bones, bones of the upper jaw, circumorbital series and occipital ring of the skull of the adult Egyptian cobra, Naja haje have been described in detail, and compared with those of the other snakes studied by the previous authors. The median dorsal bones of the cranium are the nasals, frontals, parietals, but not the premaxillae. The paired nasals are exceptionally elongated anteriorly to the extent that the premaxillae and their processus nasalis are completely hidden in a dorsal view. The paired frontals send lateral downgrowths through their whole length which unite together in the mid-ventral line just dorsal to the parasphenoid. The fused parietals also send lateral downgrowths which articulate ventrally with the posterior part of the parasphenoid and the anterior part of the basisphenoid. The upper jaw is composed only of the premaxilla, maxilla and quadrate on either side. The fused premaxillae possess a processus nasalis, and ventrafly they send backwards a palatal process. The maxilla carries two poisonous fangs and two solid small teeth. It is quite separate from the premaxilla, but connected with the palatine (through its palatal process), prefrontal and ectopterygoid. The length of the maxilla is reduced in comparison with that of the boids arid colubrids. The incomplete bony orbital ring is formed only of the prefrontal, frontal and postfrontal. Thus the jugal, lacrymal and postorbital are completely lacking, and the parietal is excluded from the circumorbital series by the presence of the postfrontal. The prefrontal extends from the cranial roof to the upper jaw. It is firmly fixed dorsally with the antero-lateral border of the frontal. Its ventral edge is firmly fixed to the dorsal surface of the maxilla and its palatal process. The antero-dorsal edge of the postfrontal is connected with the postero-lateral edge of the frontal, while its medial edge is in sutural contact with the parietal and its lateral downgrowth. The occipital ring consists of the four occipital bones; the basioccipital ventrally, the two exoccipitals laterally and dorsally, and the supraoccipital dorsally. The sutures separating these bones from one another are distinct. The two exoccipitals articulate with each other dorsally above the foramen magnum, thus excluding the supraoccipital from this foramen. The occipital condyle is tripartite formed out of the bath-occipital and the two exoccipitals. The exoccipital is completely fused, without any line of demarcation, with the opisthotic to form a compound bone which is called the otoccipital. [ABSTRACT FROM AUTHOR]

The article presents information on a study of the development of the skull of lemuroids. The author studied the development of the chondrocranium in the following stages of Loris embryos collected. Most of the regions of the chondrocraniurn are noticed as procartilaginous structures. The occipital region shows the cartilaginous arches prominently. In the posterior region of the basal plate, the occipital arches are united with the former, the hypophysial foramina piercing the occipital arches. The basal plate is cartilaginous and on either side, the procartilaginous optic capsules are noticed. In the region of the hypophysis, the basal plate continues into a broad cartilaginous plate below it and posteriorly, there is a procartilaginous crista transversa.

Notwithstanding the wide paleontological range of distribution of fossil Mustelidae and studies carried on since many years past some features of their organization have remained somewhat obscure till now. Nor is the phylogeny of Mustelidac quite clear. Transverse (occipital) crest is strong and subdivided, in its upper part, into an inner and an outer crest. Sagittal crest is by far weaker than in Gulo, and there is no large hooklike process overhanging the occipital forarnen. The distance of the occipital end of the sagittal crest to the brain is 18 mm.

This article focuses on a research on the embryogenic development of the skull of Polypterus conducted by the author. A great obstacle to an understanding of many features in the adult Polypterus has been the lack of suitable embryological stages. The current investigation was carried out in the Zootomical Institute of the University of Stockholm. The chondrocranium of one of the specimen studied was only slightly different from another studied previously. The first ossifications in the neural cranium are the sphenoid and the occipital which were already developed in this specimen.

In this part I shall try to give, as far as possible, guided by the embryological experiences, a comparative analysis of the different types of skull met with in sharks and rays. Considering that there are many gaps in our knowledge, as not all sharks and rays are investigated with regard to details of the cranium, many points must be left undecided, and it has been necessary to make some generalizations, which may subsequently perhaps be found to have been somewhat rash. For this part of my work I have dissected a number of skulls or studied a series of sections of older embryonic stages. Representatives of the following genera have been investigated: Sharks - Notidanids, Chlamydoselachid, Squaloids, Pristiophorid, Rhinid, Orectolobids, Heterodontid, and Galeoids; Rays - Pristid, Rhinobatids, Discobatid, Terpedids, Rajids, Dasybatids, and Myliobatids. A great many genera are missing from this vast list. Some of them, however, have previously been described fairly well by various authors and could thus be compared, in some respects at least, with the better known genera. As in closely allied groups, especially, in my experience, Galeoids, the differences in the principal cranial structures are very small, I think, on the whole at any rate, that the generalizations made will prove to be correct. In order to facilitate the comparison between the different groups of sharks as well as of rays, I have throughout this part enumerated the characters in the same sequence, giving to each its constant number. The characters are positive as well as negative. If, for instance, in notidanids it is said, "no paired rostral rods," such a statement is only of special interest if a comparison is made with galeoid sharks and so on. Owing to lack of space the discussions have been made very summary, but I think the reader will easily fill in the gaps. [ABSTRACT FROM AUTHOR]