Variability of branching of the a. coeliaca (truncus coeliacomesentericus) in the guinea pig (Cavia aperea f. porcellus)

The authors studied branching of the a. coeliaca (the truncus coeliacomesentericus) in a group of Peruvian short-haired guinea pigs, with special reference to its variability. After the animals had been anaesthetized, their arterial bed was injected with red-dyed latex, fixed and dissected. In all 30 guinea pigs (100%), blood was supplied to the unpaired organs of the abdominal cavity by a truncus coeliacomesentericus arising from the aorta abdominalis at fundus ventriculi level. In 53.3% of the cases, the truncus coeliacomesentericus divided into a truncus gastrolienalis sending out an a. gastrica sinistra and an a. lienalis, and to a truncus hepatomesentericus which split up into an a. hepatica communis and a. mesenterica cranialis. An a. coeliaca (tripus Halleri) was found in only one guinea pig (3.3%), as a branch of the truncus coeliacomesentericus. In the remaining cases, the truncus branched in the most varied ways. The a. gastrica sinistra was most frequently (60%) a branch of the truncus gastrolienalis. In 21 cases (70%) there was a single a. gastrica sinistra and in nine cases (30%) it was doubled. In 29 cases (96.7%) the a. hepatica communis arose from the truncus hepatomesentericus. The classic type of division of the a. hepatica communis to an a. hepatica propria and an a. gastroduodenalis was observed in every case (100%). In 100% of the cases, the a. hepatica propria terminated in a r. dexter and a r. sinister to the liver. An a. cystica, as a direct branch of the a. hepatica propria, was formed in 28 cases (93.3%). In every case (100%) the a. pancreaticoduodenalis cranialis was a branch of the a. gastroduodenalis. An a. gastrica dextra was recorded in only eight cases in the series (26.7%)--in 23.3% as a branch of the a. hepatica propria and in 3.3% as a branch of the a. cystica. Duplication of this artery was found in one case (3.3%). An a. lienalis was found in 28 cases (93.3%), as a direct branch of the truncus gastrolienalis; in two cases (6.7%) it was doubled. An a. gastroepiploica sinistra and a. gastroepiploica dextra were present in 100% of the cases. Inter-organ arterial anastomoses were found in 22 guinea pigs (73.3%)--between the spleen and the stomach (36.7%), between the pancreas and the stomach (10%), between the stomach, spleen and pancreas (10%) and, in the remaining cases, as various combinations of these connections.(ABSTRACT TRUNCATED AT 400 WORDS)     

Variability of ramification of the a. mesenterica cranialis in the domestic rabbit (Oryctolagus cuniculus f. domestica)

The authors studied the ramification of the a. mesenterica cranialis and its variability in 30 domestic rabbits (Oryctolagus cuniculus, f. domestica, breed New Zealand White). The animals were anaesthetized and red-dyed latex was injected into their arterial bed via the thoracic aorta. In every case (100%), the a. mesenterica cranialis was an independent trunk arising from the abdominal aorta 1.5-2 cm caudally to the origin of the a. coeliaca. We did not observe a truncus coeliaco-mesentericus in our material. In 17 cases (56.7%), the a. pancreaticoduodenalis caudalis was the first branch of the a. mesenterica cranialis. In 28 cases (93.3%) it formed a thick trunk which divided into two main branches to the aboral part of the duodenum and the caudal part of the pancreas respectively; in two cases (6.7%), the a. pancreaticoduodenalis caudalis was duplicated. In only two cases (6.7%), the first branch of the a. mesenterica cranialis was the a. colica media. The a. mesenterica cranialis then divided into two thick trunks to the intestine - the truncus jejunalis and the truncus ileocaecocolicus. Single aa. jejunales branched off successively from the arching truncus jejunalis. The truncus ileocaecocolicus led in a caudal direction and broke up, as a rule, into three arteries supplying the ileum, the caecum and the colon transversum. In 17 cases (56.7%), 1-6 aa. jejunales arose directly from the trunk of the a. mesenterica cranialis and 13-21 from the convexity of the arch of the truncus jejunalis. In 13 cases (43.3%), all the aa. jejunales found (11-23) were branches of the truncus jejunalis. On the mesenteric side of the jejunum, the aa. jejunales forked and formed an arcade from which small branches led to the intestine. In the rabbit we always observed only one arcade; more complex systems were not formed. A truncus ileocaecocolicus, whose branching was characterized by marked variability, was found in all 30 cases (100%). Division of this trunk to an a. ileocaecalis, a. caecocolica and a. colica dextra was observed in only four cases (13.3%). In every case, extensive anastomoses with branches of the a. colica dextra and a. colica sinistra were formed. In general, it can be claimed that the arterial bed of the a. mesenterica cranialis is highly variable. Since little attention has been paid in the literature to variability of the ramification of this artery in different species of mammals, the authors will concentrate, in their next studies, on a detailed investigation of the arterial bed of the abdominal cavity, and of its variability, in further laboratory animals.     

Morphogenesis of the truncus arteriosus of the chick embryo heart: the formation and migration of mesenchymal tissue.

The appearance and migration of mesenchymal cushion tissue within the truncus arteriosus of the normal 2.5 to 6-day chick embryo heart was surveyed systemically with the light microscope. Series of cross-sections taken from replicate hearts at successive developmental stages allowed comparison of the following qualitative and quantitative aspects of early truncal morphogenesis. Mesenchyme within the truncus was derived from two distinct sources. The first mesenchyme appeared to migrate caudally into the cardiac jelly of the distal truncus from the nearby aortic arch region, coincident with slowing of the anterior elongation of the heart tube (Hamburger-Hamilton Stage 17-18). A second, separate mesenchymal population, derived from endocardium, began to fill the conus and proximal truncus in a radial direction, coicident with expansion of the bulbs cordis (Stage 12-19). The measured kinetics of relative cell numbers, distributions, and mitotic indices suggest substantial contributions from both sources. By Stage 26, the conotruncal region was filled with mesenchyme, which then condensed to form the anlagen of three future structures: the semilunar valves, the aorticopulmonary septum, and the tunica media of the great arteries.     

Localization of choline acetyltransferase in human brain stem neurons

Berth's method was used to study the cytochemical activity of choline acetyltransferase in truncus cerebri neurons of 6-8 lunar month-old human fetuses. Three types on neurons were diagnosed in the nuclei of the truncus cerebri with regard to cholinacetyltransferase localization: (1) cholinergic cholinoceptive neurons; (2) cholinergic non-cholinoceptive neurons; (3) non-cholinergic cholinoceptive neurons. The distribution of the neurons in 27 nuclei of the truncus cerebri is described.     

Phylogenetic implications of the morphology of the braincase of caecilian amphibians (Gymnophiona)

Caecilian morphology is strongly modified in association with their fossorial mode of life. Currently phylogenetic analyses of characters drawn from the morphology of caecilians lack resolution, as well as complementarity, with results of phylogenetic analyses that employ molecular data. Stemming from the hypothesis derived from the mammal literature that the braincase has the greatest potential (in comparison to other cranial units) to yield phylogenetic information, the braincase and intimately associated stapes of 27 species (23 genera) of extant caecilians were examined using images assembled via microcomputed tomography. Thirty‐four new morphological characters pertaining to the braincase and stapes were identified and tested for congruence with previously recognized morphological characters. The results reveal that when added to previous character matrices, characters of the braincase and stapes resolve generic‐level relationships in a way that is largely congruent with the results of molecular analyses. Analysis of a combined data set of molecular and morphological data provides a framework for conducting ancestral character state reconstructions, which resulted in the identification of 95 new synapomorphies for various clades and taxa, 27 of which appear to be unique for the taxa that possess them. Together these data demonstrate the utility of the application of characters of the braincase and stapes for resolving phylogenetic relationships for a group whose morphology is largely confounded by functional modifications. In addition this study provides evidence of the utility of the braincase in resolving problematic morphology‐based phylogeny outside of Amniota, in an amphibian group. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166 , 160–201.     

Course and branches of the recurrent laryngeal nerve, inferior thyroid artery and inferior laryngeal artery

Length, width, and thickness of the recurrent laryngeal nerve and its extra-laryngeal twigs were estimated. Included is the course of the nerve to the suspensory ligament of the thyroid gland, to the inferior horn of the thyroid cartilage and to trachea and esophagus. The origin of the inferior thyroid artery, its width and course to the twigs of the recurrent laryngeal nerve were studied. The origin zone of the inferior laryngeal artery is also described. The different terms and opinions about the twigs of the truncus thyreocervicalis and the thyroid axis are discussed.     

Bone‐conduction hearing and seismic sensitivity of the late permian anomodont Kawingasaurus fossilis

An investigation of the internal cranial anatomy of the anomodont Kawingasaurus from the Upper Permian Usili Formation in Tanzania by means of neutron tomography revealed an unusual inner and middle ear anatomy such as extraordinarily inflated vestibules, lateroventrally orientated stapes with large footplates, and a small angle between the planes of the anterior and lateral semicircular canals. The vestibule has a volume, which is about 25 times larger than the human vestibule, although Kawingasaurus has only a skull length of approximately 40 mm. Vestibule inflation and enlarged stapes footplates are thought to be functionally correlated with bone‐conduction hearing; both morphologies have been observed in fossorial vertebrates using seismic signals for communication. The firmly fused triangular head with spatulate snout was probably used for digging and preadapted to seismic signal detection. The quadrate‐quadratojugal complex was able to transmit sound from the articular to the stapes by small vibrations of the quadrate process, which formed a ball and socket joint with the squamosal. Mechanical considerations suggest that the ventrolaterally orientated stapes of Kawingasaurus was mechanically better suited to transmit seismic sound from the ground to the fenestra vestibuli than a horizontal orientated stapes. The low sound pressure level transformer ratio of 2–3 in Kawingasaurus points to a seismic sensitivity of the middle ear and a vestigial or reduced sensitivity to airborne sound. Three hypothetical pathways of bone conduction in Kawingasaurus are discussed: 1) sound transmission via the spatulate snout and skull roof to the otic capsules, 2) relative movements resulting from the inertia of the mandible if sound is percepted with the skull, and 3) bone conduction from the substrate via mandible, jaw articulation, and stapes to the inner ear. J. Morphol. 276:121–143, 2015. © 2014 Wiley Periodicals, Inc.     

The stapes of the Goal Measures embolomere Pholiderpeton scutigerum Huxley (Amphibia: Anthracosauria) and otic evolution in early tetrapods

Middle ear structure has been of interest for a long time in studies of the origins and relationships of early tetrapod groups. The model of a dorsally-directed, rod-like stapes with a tympanum, thought common to labyrinthodont amphibians, was taken to be primitive for tetrapods. The stapes of embolomeres and other early anthracosaurs were assumed to be of this form, but difficulties resulted if the middle ear structure of fossil and living reptiles was considered ultimately derived from this source.
The embolomere stapes has been identified and does not conform to the predicted model. It most closely resembles that of Greererpeton , an early notchless temnospondyl. The stapes is compared with those of other tetrapods in terms of the theoretical five processes. An interpretation is put forward in which all but the opercular are seen as potentially present. The embolomere stapes is compared with that of Greererpeton in terms of recent theories of mechanical function and is seen to weaken them. They are then compared as part of a possible acoustic mechanism. The embolomere middle ear structure is reinterpreted as a receiver for low-frequency sound and the 'otic notch' is not considered to have housed a tympanum.
The resemblance between the stapes of these two animals seems best explained by their closeness to the plesiomorphic condition for tetrapods, a conclusion which forces the abandonment of the concept of a 'labyrinthodont middle ear'. The middle ear structure of later groups can be interpreted as having evolved from one similar to that seen in these two animals. The conclusion supports those reached in other recent papers that tympana were not primitive for tetrapods but have been independently derived in several groups.     

Pathogenesis of persistent truncus arteriosus induced by nimustine hydrochloride in chick embryos

Nimustine hydrochloride (ACNU) is a nitrosourea derivative anticancer agent which has been shown to cause persistent truncus arteriosus in chick embryos. The objective of this study was to confirm the teratogenic effects of ACNU on the cardiovascular system of chick embryos and to determine whether ACNU induces persistent truncus arteriosus by interfering with neural crest cells. Various doses of ACNU ranging from 10 to 200 micrograms were injected under the chorioallantoic membrane of chick embryos on the third day of incubation. Saline solution was used as the control. After 10 to 11 days of incubation, 242 (46%) survivors of the 524 treated eggs were obtained. The survival rates of the embryos and the frequencies of cardiovascular anomalies were dose dependent. Of 146 embryos with cardiovascular anomalies, 104 (71%) had persistent truncus arteriosus. Ventricular septal defect and double-outlet right ventricle were seen in 37 (25%) and one (1%), respectively. Aortic arch anomalies were seen in 116 embryos (79%). Quail-chick chimeras (chick embryos with quail cardiac neural crest) were treated with 50 micrograms of ACNU and examined histologically 24 hours later. These chimeras showed dying neural crest cells in the pharyngeal arches. Dying cells were also noted in the neural tube, cranial ganglia, retina, and otocyst. These results suggest that persistent truncus arteriosus in chick embryos treated with ACNU is induced by neural crest cell death.     

Incudomalleal joint formation: the roles of apoptosis,migration and downregulation

Background  

The middle ear of mammals is composed of three endochondrial ossicles, the stapes, incus and malleus. Joints link the malleus to the incus and the incus to the stapes. In the mouse the first arch derived malleus and incus are formed from a single Sox9 and Type II collagen expressing condensation that later subdivides to give rise to two separate ossicles. In contrast the stapes forms from a separate condensation derived from the second branchial arch. Fusion of the malleus and incus is observed in a number of human syndromes and results in conductive hearing loss. Understanding how this joint forms during normal development is thus an important step in furthering our understanding of such defects.     

Feasibility of using the national hospital discharge survey to estimate the prevalence of selected birth defects

BACKGROUND: Nationally representative data on the prevalence of certain birth defects are largely unavailable. We evaluated the feasibility of using data from the National Hospital Discharge Survey (NHDS) to describe the prevalence of selected birth defects. METHODS: All live births recorded in the NHDS during 1999-2001 were included. The prevalence for selected birth defects was calculated using weighted ratio estimators. Prevalence ratios comparing the NHDS estimates to published national estimates from the National Birth Defects Prevention Network (NBDPN) were calculated. RESULTS: With the exception of common truncus, the NHDS prevalence for the selected defects was consistently lower than the NBDPN estimates. The prevalence ratios ranged from 0.38 for trisomy 18 and anopthalmia/micropthalmia to 1.16 for common truncus. The NHDS prevalence estimates for spina bifida without anencephaly (PR 0.89, 95% CI: 0.57-1.22) and gastroschisis/omphalocele (PR 0.94, 95% CF: 0.48-1.40) most closely approximated the NBDPN estimates. CONCLUSIONS: NHDS data underestimate the prevalence of most birth defects. Additional research is needed to determine whether NHDS estimates may be useful for evaluating trends in certain conditions. Surveillance systems employing active case-finding continue to provide more accurate estimates of birth defects prevalence.     

Early changes in GABA and glutamate levels and aminotransferase activity in parts of the rat brain following whole-body gamma irradiation at an absolutely lethal dose

The contents of gamma-aminobutyric acid (GABA) and glutamate (GL) as well as GABA-aspartate- and alanine aminotransferase activities were measured in rat cerebellum, cerebral cortex and truncus cerebri 1, 3, 6, 24 and 48 hr following total-body gamma-irradiation (60Co) with a dose of 30 Gy. All the indices under study changed in a similar way in the cortex and truncus cerebri while in the cerebellum, GABA level increased and GABA-alpha-ketoglutarate aminotransfearse activity decreased 60 min after irradiation. The levels of GABA and GL in the cortex and truncus cerebri decreased immediately and increased 24 hr after irradiation. Activity of aminotransferases changed in a phase manner: changes in aspartate- and alanine aminotransferase activity were more pronounced than those of GABA-alpha-ketoglutarate aminotransferase activity and correlated with the glutamate level changes.     

Ear ossicle morphology of the Jurassic euharamiyidan Arboroharamiya and evolution of mammalian middle ear

The middle ear bones of Mesozoic mammals are rarely preserved as fossils and the morphology of these ossicles in the earliest mammals remains poorly known. Here, we report the stapes and incus of the euharamiyidan Arboroharamiya from the lower Upper Jurassic (～160 Ma) of northern China, which represent the earliest known mammalian middle ear ossicles. Both bones are miniscule in relation to those in non‐mammalian cynodonts. The skull length/stapedial footplate diameter ratio is estimated as 51.74 and the stapes length as the percentage of the skull length is 4%; both numbers fall into the stapes size ranges of mammals. The stapes is “rod‐like” and has a large stapedial foramen. It is unique among mammaliaforms in having a distinct posterior process that is interpreted as for insertion of the stapedius muscle and homologized to the ossified proximal (stapedial) end of the interhyal, on which the stapedius muscle attached. The incus differs from the quadrate of non‐mammalian cynodonts such as morganucodontids in having small size and a slim short process. Along with lack of the postdentary trough and Meckelian groove on the medial surface of the dentary, the ossicles suggest development of the definitive mammalian middle ear (DMME) in Arboroharamiya. Among various higher‐level phylogenetic hypotheses of mammals, the one we preferred places “haramiyidans” within Mammalia. Given this phylogeny, development of the DMME took place once in the allotherian clade containing euharamiyidans and multituberculates, probably independent to those of monotremes and therians. Thus, the DMME has evolved at least three times independently in mammals. Alternative hypothesis that placed “haramiyidans” outside of Mammalia would require independent acquisition of the DMME in multituberculates and euharamiyidans as well as parallel evolution of numerous derived similarities in the dentition, occlusion pattern, mandibles, cranium, and postcranium between the two groups and between “haramiyidans” and other mammals. J. Morphol. 279:441–457, 2018. © 2016 Wiley Periodicals, Inc.     

The braincase and middle ear region of Dendrerpeton acadianum (Tetrapoda: Temnospondyli)

Dendrerpeton acadianum from the Westphalian A (Upper Carboniferous) of Joggins, Nova Scotia, is a phylogenetically and chronologically early temnospondyl. Its external cranial anatomy has been used previously to suggest the presence of a tympanic membrane, and thus of an ear adapted to the perception of airborne sound. However, supporting evidence provided by stapedial and braincase morphology has so far been lacking. The braincase and middle ear region have remained almost wholly unknown. CT scanning and 3-D computer reconstruction of BMNH R.436 have been used to shed light on these important areas. Both stapes prove to be present in the specimen; the right stapes is distorted, but the left stapes lies inside the cranial cavity and is perfectly preserved. The latter resembles the stapes of the relatively few other temnospondyls in which the bone has been described and is most similar to that of Doleserpeton . The morphology and orientation of the stapes provide strong evidence for the presence of an ear adapted to the perception of airborne sound, with similarities to the extant anuran condition. The reconstructed braincase shows a high degree of similarity to that of other adequately known temnospondyls. This gives supporting evidence that D. acadianum is correctly placed in the temnospondyl phylogeny and thus demonstrates one of the earliest hearing systems adapted to the perception of airborne sound that can be homologized with the extant anuran condition.  © 2005 The Trustees of the Natural History Museum, Zoological Journal of the Linnean Society , 2005, 143 , 577−597.     

Ear Disease in Skulls From the Sully Burial Site

Abstract

A study was made of 358 skulls (255 Arikara from a single burial area) visually and with X-rays looking for evidence of disease in and about the ears with special reference to infection and OTOSCLEROSIS with fixation of the stapes footplate. No stapes fixation was found. X-rays showed altered mastoid cell development in 139 of 255 ears (55o/o). Osteomas were found in l 7 external auditory canals of ll individuals (3. Oo/o).     

Reexamination of the morphological evidence for the cohort Epitheria (Mammalia,Eutheria)

Novacek and co-workers recognized a monophyletic clade Epitheria, comprising all eutherians except edentates and the extinct palaeoryctoids, on the basis of two synapomorphies: a stirrupshaped stapes and a foramen ovale enclosed within the alisphenoid. To evaluate this phylogenetic hypothesis, we reexamined the distributions of stapedial morphologies and positions of the foramen ovale across Recent and extinct mammals and nonmammalian cynodonts. The states and distributions of the stapes and forament ovale characters used by Novacek and coworkers were modified by recognizing two stapedial characters (one relating to shape of the crura, the other to the nature of the foramen) and a single, multistate foramen ovale character (within, behind, and lateral to the alisphenoid). The taxon-character matrix used by Novacek (1989, 1992b), substituting our amended stapedial and foramen ovale characters and adding several previously unscored extinct taxa and three new characters, was subjected to a series of PAUP manipulations. Identified among the most parsimonious trees were three major topologies for the base of Eutheria: (1) a polytomy including an Edentata/Ungulata clade, (2) a polytomy with Edentata and Ungulata as separate clades, and (3) Edentata and (when included) Palaeoryctoidea as the successive outgroups to a monophyletic Epitheria. We conclude that topology 2 best reflects the current state of knowledge. An edentate/ungulate clade is supported by three characters (from the mastoid region and subarcuate fossa); however, other morphological studies require modification of the distributions of these characters in xenarthrans and bassal ungulates, thereby eliminating support for this clade. In nearly all manipulations, obtaining a monophyletic Epitheria required that one or two steps be added to the most parsimonious trees. When a monophyletic Epitheria was obtained, it was supported by a triangular stapes and, in some trees, the reappearance of a stapedial artery (lost earlier at the level of Recent therians) and a transpromontorial internal carotid artery. In the most parsimonious trees, a foramen ovale within the alisphenoid was an equivocal synapomorphy of Recent therians or cutherians, and a stapes with strongly convex crura (our state closest to the stirrup-shaped state of Novacek and co-workers) appeared independently within various eutherian lineages. The reduction or loss of the stapedial foramen was identified as an independent event in monotremes and within marsupials and various eutherian lineages.To whom correspondence should be addressed.     

On the neurons with dendrites intermingling with the fibers of the human corpus callosum: a Golgi picture

Golgi preparations of the anterior part of the truncus of the corpus callosum from 11 adult human brains were investigated. The vertical plane of section was situated symmetrically between the frontal and sagittal plane. The use of this oblique plane of section enabled easy identification of the neurons with dendrites intermingling with transcallosal fibers, what was not possible in standard frontal sections. 2 types of such neurons (with features of other interstitial neurons) were described: fusiform and multipolar. Both types of neurons were more frequently impregnated in areas adjacent to induseum griseum, cingular cortex, and in the depth of the callosal sulcus. Multipolar neurons were also present in the central core and in ventral parts of the corpus callosum, but fusiform ones were not present in ventral parts of the corpus callosum truncus. The dentrites of both types of neurons usually were perpendicular to, sometimes also parallel to transcallosal fibers. The impregnation of these neurons in groups and pairs suggest their integrative role, and their planar orientation in mentioned oblique plane corresponds to oblique direction of transcallosal cingulostriatal decussating fibers.     

白暨豚气管和肺的解剖和组织学的研究

白鱀豚的肺分左右2叶,不分小叶,肺门位置高。气管分叉成左右主支气管和气管支气管,气管支气管分叉点的位置较高,情形与拉河豚相近。3条主支气管进入肺以后便成为肺内支气管树的主干,其分支的分布区可暗示假定肺叶的存在(共5叶,左2右3)。从气管起一直到呼吸性支气管都存在软骨组织。气管的粘膜上皮为假复层纤毛柱状上皮,夹有杯状细胞。主支气管为单层柱状上皮,无杯状细胞。小支气管和细支气管又变为假复层纤毛柱状上皮,杯状细胞少。细支气管以下逐步改变为单层柱状上皮和立方上皮。各级支气管均未见腺体存在。从呼吸性细支气管到肺泡管的通道口,有括约肌存在。各级支气管一直到肺泡壁均有平滑肌存在,从断续出现到连续的环层。弹性纤维在整个气管均很丰富。       

Evolution of the mammalian middle ear.

The structure and evolution of the mandible, suspensorium, and stapes of mammal-like reptiles and early mammals are examined in an attempt to determine how, why, and when in phylogeny the precursors of the mammalian tympanic bone, malleus, and incus (postdentary jaw elements and quadrate) came to function in the reception of air-borne sound. The following conclusions are reached: It is possible that at no stage in mammalian phylogeny was there a middle ear similar to that of "typical" living reptiles, with a postquadrate tympanic membrane contracted by an extrastapes. The aquamosal sulcus of cynodonts and other therapsids, usually thought to have housed a long external acoustic meatus, possibly held a depressor mandibulae muscle. In therapsids an air-filled chamber (recessus mandibularis of Westoll) extended deep to the reflected lamina and into the depression (external fossa) on the outer aspect of the angular element. A similar chamber was present in sphenacodontids but pterygoideus musculature occupied the small external fossa. The thin tissues superficial to the recessus mandibularis served as eardrum. Primitively, vibrations reached the stapes mainly via the anterior hyoid cornu, but in dicynodonts, therocephalians, and cynodants vibrations passed mainly or exclusively from mandible to quadrate to stapes and the reflected lamina was a component of the eardrum. In the therapsid phase of mammalian phylogeny, auditory adaptation was an important aspect of jaw evolution. Auditory efficiency, and sensitivity to higher sound frequencies were enhanced by diminution and loosening of the postdentary elements and quadrate, along with transference of musculature from postdentary elements to the dentary. These changes were made possible by associated modifications, including posterior expansion of the dentary. Establishment of a dentary-squamosal articulation permitted continuation of these trends, leading to the definitive mammalian condition, with no major change in auditory mechanism except that in most mammals (not monotremes) the angular, as tympanic, eventually bcame a non-vibrating structure.     

Development and evolution of the carotid circulation in geomyoid rodents in relationship to their craniomorphology

The diversity in cranial morphology of living geomyoids, including pocket gophers (Thomomys), spiny pocket mice (Heteromys and Liomys), desert pocket mice (Chaetodipus and Perognathus), and kangaroo rats and mice (Dipodomys and Microdipodops) is accompanied by only a few differences in their cephalic arterial circulation. The principal difference is the origin of the pterygopalatine artery, which serves the orbit and rostrum. In dipodomyines and perognathines it originates as a stapedial branch of the internal carotid artery and passes through the middle ear en route to the braincase. In geomyines and heteromyines it originates as an internal maxillary branch of the external carotid artery and enters the braincase directly. Either geomyines and heteromyines are convergent in this respect, or the currently recognized family Heteromyidae is paraphyletic. The stapedial artery is the same size in early embryos of T. bottae and D. merriami, but in the former species it fails to grow and disappears in juveniles. Comparison of developmental series of D. merriami and T. bottae revealed that the decline of the artery in the latter species is preceded by a greater degree of arterial coarctation, or narrowing, as it passes though the developing stapes. The loss of the stapedial artery is correlated with an enlarged masseter profundus muscle in T. bottae and with an unusually small stapes in T. bottae, H. desmarestianus, and L. salvini. I hypothesize that the primitive condition for geomyoids is the presence of both stapedial and internal maxillary arteries, that the stapedial artery was lost in geomyines and heteromyines because of the constraint on its size posed by the stapes, and that the stapedial artery was retained in dipodomyines because enlargement of the stapes accompanied bullar inflation in these taxa and lifted the constraint on the size of the stapedial artery.