Patterning of the cranial nerves in the chick embryo is dependent on cranial mesoderm and rhombomeric metamerism

The vertebrate peripheral nervous system (PNS) consists of two groups of nerves that have a metamerical series of proximal roots along the body axis: the branchial and spinal nerves. Spinal nerve metamerism is brought about by the presence of somites, while that of the branchial nerves is, in part, intrinsic to rhombomeres, the segmental compartments of the hind-brain. As the distribution pattern of neural crest cells prefigures the morphology of the PNS, we constructed tissue-recombinant chick embryos in order to determine factors that might regulate the crest cell distribution pattern. When the segmental plate was transplanted between the hind-brain and the head mesoderm before crest cell emigration, it developed into ectopic somites that inhibited the dorsolateral migration of crest cells such that formation of the cranial nerve trunks was disturbed. Even so, proximal portions of the nerve roots were intact. An ectopic graft of lateral mesoderm did not inhibit the directional migration of the crest cells, but allowed their ectopic distribution, resulting in the fusion of cranial nerve trunks. When spinal neurectoderm was transplanted into the hind-brain, the graft behaved like an even-numbered rhombomere and caused the fusion of cranial nerve roots. The identity of the spinal neurectoderm was preserved in the ectopic site analyzed by the immunolocalization of Hoxb-5 protein, a spinal cord marker. We conclude that the spatial distribution of cephalic crest cells is regulated by successive processes that act on their proximal and distal distribution. The migratory behavior of crest cells is achieved partly by an embryonic environment that is dependent upon the presence of somitomeres, which do not epithelialize as somites, in the trunk.     

Cranial anomaly of homozygous rSey rat is associated with a defect in the migration pathway of midbrain crest cells

Craniofacial development of vertebrates depends largely on neural crest contribution and each subdomain of the crest-derived ectomesenchyme follows its specific genetic control. The rat small eye ( rSey ) involves a mutation in the Pax-6 gene and the external feature of rSey homozygous embryos exhibits craniofacial defects in ocular and frontonasal regions. In order to identify the mechanism of craniofacial development, we examined the cranial morphology and migration of cephalic crest cells in rSey embryos. The chondrocranial defects of homozygous rSey embryos primarily consisted of spheno-orbital and ethmoidal anomalies. The former defects appeared to be brought about by the lack of the eye. In the ethmoid region, the nasal septum and the derivative of the medial nasal prominence were present, while the rest of the nasal capsule, as well as the nasal and lachrymal bones, were totally absent except for a pair of cartilaginous rods in place of the nasal capsule. This suggests that the primary cranial defect is restricted to the lateral nasal prominence derivatives. Dil labeling revealed the abnormal migration of crest cells specifically from the anterior midbrain to the lateral nasal prominence in homozygous rSey embryos. Pax-6 was not expressed in the crest cells but was strongly expressed in the frontonasal ectoderm. To determine whether or not this migratory defect actually resides in environmental cues, normal midbrain crest cells from wild-type embryos were labeled with Dil and were orthotopically injected into host rSey embryos. Migration of the donor crest cells into the lateral nasal prominence was abnormal in homozygous host embryos, while they migrated normally in wild-type or heterozygous embryos. Therefore, the cranial defects in rSey homozygous embryos are due to inappropriate substrate for crest cell migration towards the lateral nasal prominence, which consistently explains the cranial morphology of homozygous rSey embryos.     

Myology of the Feeding Apparatus of Myrmecophagid Anteaters (Xenarthra: Myrmecophagidae)

The musculoskeletal feeding apparatus of anteaters in the family Myrmecophagidae (Eutheria: Xenarthra) is described, compared among the three extant genera (Tamandua, Myrmecophaga, Cyclopes), and interpreted in a phylogenetic framework. Character polarities are assessed with reference to other xenarthrans, eutherians, and didelphid marsupials. Xenarthrans are widely regarded as basal eutherians, and this is reflected in the apparent retention of plesiomorphic character states in jaw and pharyngeal musculature. Jaw closing muscles are architecturally simple, the stylohyoideus is absent, the stylopharyngeus is robust and architecturally complex, and the superior pharyngeal constrictor is weak. At the same time, the highly specialized trophic ecology of myrmecophagids is reflected in derived features of the jaw, tongue, and palatal musculature. The sternomandibularis is present, the tongue is largely composed of a sternog-lossus with no attachments to the hyoid apparatus, other glossus muscles are modified and do not enter the tongue, and the mylohyoideus and stylopharyngeus contribute to the soft palate, while other palatal muscles vary among the myrmecophagid genera. Feeding apparatus mycology provides further support for myrmecophagid monophyly. Documentation of the morphological transformations that lead to the myrmecophagid condition is hampered by incomplete data on feeding apparatus structure in nonmyrmecophagid xenarthrans (sloths and armadillos) but a tentative character mapping onto an independently derived phylogeny is offered.     

Sexual dimorphism in striped dolphin (Stenella coeruleoalba) crania from South Africa

This study assessed the extent of sexual dimorphism in striped dolphin (Stenella coeruleoalba) cranial size and shape off the South African coast. Dorsal and ventral features of 60 striped dolphin crania from both the western and eastern coasts of South Africa were analyzed using landmark‐based geometric morphometrics. Although there was no evidence of dimorphism in cranial size, evidence for small, but significant, variation in both dorsal and ventral cranial shape was found between the sexes. The observed dimorphism was partly associated with changes in shape around the temporal fossa, occipital condyle and supraoccipital bone, the nasal bone, and the paraoccipital process and basiocciptal. The temporal fossa serves as an attachment point for the temporal muscle, which functions to close the lower jaw, and the occipital area serves as the anterior insertion of the epaxial muscles, which power the upstroke of the flukes during swimming. Both the paraoccipital process and basiocciptal are associated with the functioning of the hyoid apparatus, which serves as an attachment point for muscles and ligaments involved in feeding and sound production. These findings suggest the possibility of differences in diet, foraging behavior, vocalizations, and locomotion between the sexes of this species.     

Real-time measurement of RFR energy distribution in the macaca mulatta head

Temperature increases due to absorption of 1.2 GHz, CW, 70 mW/cm², radio frequency (RF) energy, were measured in 3.3-cm-radius homogeneous muscle-equivalent spheres, M. mulatta cadaver heads (both detached from and attached to the body) and living, anesthetized M. mulatta heads. Temperatures were measured with a Vitek, Model 101 Electrothermia Monitor and temperature distributions were compared to theoretical predictions from a thermal-response model of a simulated cranial structure. The results show that the thermal response model accurately predicts the temperature distribution in muscle-equivalent spheres, the distribution of temperature in detached M. mulatta heads when exposed from the back of the head, and the distribution of temperature in attached M. mulatta cadaver heads for animals oriented with body parallel to the H-field. The temperature distribution in the detached M. mulatta heads varies markedly with exposure orientation, ie, facing forward, backward, or to the side. The orientation of the M. mulatta cadaver body significantly affects the temperature distribution in the head - with H-field orientation showing high, nonuniform values, and E-field orientation showing low, uniform values. In live animals blood flow produces a significant short-term effect on the temperature distribution in the midbrain, but not the cortex. Midbrain temperatures are both significantly higher and lower than the comparable cadaver measurements, depending on location.     

Cranial capacity estimations of the FrankfurtPan troglodytes verus collection

Cranial capacity measurements of 18 individuals (9 ♂, 9 ♀) of a total collection of 277Pan troglodytes verus skulls were taken using four different methods:- two conventional filling methods and two mathematical methods. The two mathematical analyses normally used in hominids, were for the first time specifically modified forPan. The results probably present a more accurate estimation of total cranial capacity inPan and specifically inPan troglodytes verus (352 cm³) than previously available. Sexual differences related to this trait were also measured. Regardles of the methods used,Pan troglodytes verus seems to manifest the smallest cranial capacity of all subspecies ofPan.     

Evidence that vasoactive intestinal polypeptide is a dilator transmitter to some cerebral and extracerebral cranial arteries

Many arteries of the head upon electrical stimulation of the non-adrenergic nerve terminals present in their wall exhibit dilation that is only partially reduced by atropine. The results of three types of experiments are presented that tend to implicate vasoactive intestinal polypeptide (VIP) a known vasodilator, as an atropine-resistant dilator transmitter. VIP activity is high in vessels that exhibit neurogenic dilation and low in those that do not. It is released from two arteries that show such dilation upon neurogenic field stimulation and VIP antiserum reduces neurogenic dilation. It is proposed that VIP as well as acetylcholine are released from the innervation of some cranial arteries and together in a number of animals of least are responsible for part of the complex neurogenic dilation witnessed in these vessels. Although substance P is present in nerves found within the wall of cerebral and other cranial blood vessels, it is either ineffective as a dilator in vessels that show a sizeable dilation to electrical stimulation, or else exhibits marked, rapid, persistent tachyphylaxis.