Sensory nerve endings in the hard palate and papilla incisiva of the goat

The sensory innervation of the papilla incisiva in the hard palate of the domestic goat was studied with light and electron microscopy, supplemented by electrophysiological studies of free nerve endings. The goat lacks incisor teeth. Grass and leaves are not bitten, but pulled off by pressing them between the tongue and papilla incisiva. Thus, the masticatory mucosa is subject to particularly heavy mechanical loads requiring functional specialization of the horny epithelium in the form of thickening, i.e., the papilla incisiva and 12-14 pairs of rugae palatinae. A thin layer of firm connective tissue (lamina propria) attaches the mucosa to the periost of the hard palate. Sensory nerve fibers were found most abundantly in the papilla incisiva. Their number decreased drastically in aboral direction. A section through the first four rugae palatinae contains only about 10% of the number of free nerve endings found in the same area of mucosa from the papilla incisiva. Four types of sensory nerve endings were found. Free nerve endings were seen ubiquitously in the epithelium and superficial layer of the lamina propria. Merkel nerve endings were found in the bases of the epithelial thickenings in the papilla incisiva and rugae palatinae. Few Ruffini corpuscles were found in the deeper layer of the lamina propria, while lamellated corpuscles were seen just below the basement membrane of the epithelial pegs. Thus, a variety of sensory nerve endings were found in the hard palate, especially in those areas that are in close contact with the tongue during chewing of food. This rich innervation suggests an important role in monitoring the mechanical properties of food. Recordings were made from cell bodies supplying these terminals. Classic low-threshold, slowly adapting responses were observed in Ass afferent populations. This activity was probably mediated by Merkel type endings. Alternately, high-threshold and suprathreshold responses obtained from Adelta category afferents were likely to be nociceptive. In support of this, threshold and suprathreshold sensitization was observed following injection of serotonin into the receptive field of Adelta populations. This activity was likely to be derived from the aforementioned free nerve endings.     

Mechanoreceptors of the hard palate of the mongolian gerbil include special junctions between epithelia and meissner lamellar cells: A comparison with other rodents

As a part of our comparative morphological study of mechanoreceptors in rodent oral mucosae, the hard palate of the mongolian gerbil (a kind of sand rat) was investigated by light and electron microscopy. Subepithelial connective tissue papillae of palatine rugae contained a dense distribution of lamellated corpuscles that showed an ultrastructure similar to that of Meissner corpuscles of primates. The corpuscles in the palate of the mongolian gerbil, however, frequently formed compound large corpuscles with a palisade-like extension. Antemolar rugae predominated in containing such compound “Meissner” corpuscles. Superficial cytoplasmic lamellae of the corpuscles closely adhered to overlying epithelial cells without an intervening basal lamina. Although a small number of simple corpuscles was seen in the first antemolar ruga, no similar corpuscles were encountered in other parts of the palate. On the other hand, numerous Merkel cellnerve endings were seen in epithelial pegs and sometimes in epithelial ridges of palatine rugae. Quinacrine labelling showed that intermolar rugae contained a rather dense distribution of Merkel cells in comparison with antemolar rugae. The present and previous data indicate that the pattern of palatine mechanoreceptors of the mongolian gerbil is analogous to that of the mouse, but not of the rat.     

Immunohistochemical demonstration of nerve terminals in the whole hard palate of rats by use of an antiserum against protein gene product 9.5 (PGP 9.5)

Sensory innervation of the entire hard palate was investigated in the rat using serial sections immunostained for protein gene product 9.5 (PGP 9.5), a neuronal marker. PGP 9.5-immunoreactive nerve endings were widely distributed in the hard palate, but the innervation pattern and density differed among portions. They were numerous at papillary protrusions including the incisal papilla, antemolar/intermolar rugae, and postrugal filiform papillae. Immunoreactive free nerve endings gathered at the summits of the connective tissue papillae, some of them entering deeply into the epithelium. Electron microscopy demonstrated that nerves in the postrugal filiform papillae reached the stratum corneum. The atrial region, possibly the most sensitive in the hard palate, showed unique innervation: its anterior part, adjacent to incisors, developed intraepithelial networks of fine and beaded nerves, whereas its posterior part revealed cone-shaped nerve terminals formed on the connective tissue papillae of the atrial folds which comprised two lines of longitudinal flaps. Taste bud-like corpuscles gathered in the medial walls of the incisal canals and in the "Geschmacksstreifen" (taste stripes) present at the most anterior part of the soft palate. The hard palate of the rat is thus richly innervated, and is characterized by region-specific nerve endings which may be involved in mechano- and chemoreception in the oral cavity.     

Mechanoreceptors of the hard palate of the Mongolian gerbil include special junctions between epithelia and Meissner lamellar cells: a comparison with other rodents.

As a part of our comparative morphological study of mechanoreceptors in rodent oral mucosae, the hard palate of the mongolian gerbil (a kind of sand rat) was investigated by light and electron microscopy. Subepithelial connective tissue papillae of palatine rugae contained a dense distribution of lamellated corpuscles that showed an ultrastructure similar to that of Meissner corpuscles of primates. The corpuscles in the palate of the mongolian gerbil, however, frequently formed compound large corpuscles with a palisade-like extension. Antemolar rugae predominated in containing such compound "Meissner" corpuscles. Superficial cytoplasmic lamellae of the corpuscles closely adhered to overlying epithelial cells without an intervening basal lamina. Although a small number of simple corpuscles was seen in the first antemolar rugae, no similar corpuscles were encountered in other parts of the palate. On the other hand, numerous Merkel cell-nerve endings were seen in epithelial pegs and sometimes in epithelial ridges of palatine rugae. Quinacrine labelling showed that intermolar rugae contained a rather dense distribution of Merkel cells in comparison with antemolar rugae. The present and previous data indicate that the pattern of palatine mechanoreceptors of the mongolian gerbil is analogous to that of the mouse, but not of the rat.     

The sensory innervation of the rat rhinarium

The present study documents the characteristics of innervation of the rhinarium or hairless rat snout skin by light and electron microscopy. The outer glabrous surface is covered with a stratified squamous epithelium that forms both rete pegs and rete ridges, the latter on the inferior border near the philtrum. The glabrous skin contains numerous presumptive epidermal and dermal free nerve endings (FNE's), Merkel terminals at the base of the rete ridges and pegs, and simple, nonencapsulated corpuscles. A second region of dense innervation, found on an elevation of the inner wall of the vestibule, contains similar components of innervation, with the exception that no Merkel terminals were identified. Since no Merkel terminals were present in this area of the vestibule, intraepidermal as well as dermal FNE's could be identified with certainty. This skin is covered by a thin squamous epithelium overlying dense connective tissue. The simple corpuscles are similar to those in the rhinarium, as well as resembling those described in other species. FNE's were frequently observed intimately associated with simple corpuscles. Several examples of large FNE's with two to three layers of cytoplasmic lamellae were found, suggestive of transitional forms between FNE's and simple corpuscles. Thus, the pattern of sensory innervation in the glabrous rat snout skin is similar to that found in other furred species described to date, but in addition, the sensory innervation of ridged skin in the rat also resembles that of epidermis organized into rete pegs. This dense sensory innervation may be correlated with whisking behavior of the predominantly nocturnal rat.     

Ultrastructures of mechanoreceptors in the oral mucosa

The present review describes the fine structures of lamellated mechanoreceptive corpuscles, Merkel cell-neurite complexes and free nerve endings in the oral mucosae of mammals, with special attention to axon terminals and lamellar cells. The mechanoreceptive nerve endings of the oral mucosa were studied using histochemistry, immunohistochemistry and transmission electron microscopy techniques. The organized mechanoreceptive corpuscles are present in the mucosae of gingiva, cheek, tongue and soft and hard palate. They are elongated or globular in shape, being located in the connective tissue papillae. The capsule is composed of several layers of cytoplasmic extensions of perineural cells. Numerous bundles of collagen fibers are noted at the periphery of the corpuscle. The lamellated corpuscles are surrounded by several layers of superimposed flattened capsular cell processes. The interlamellar spaces are 0.2-0.4 micron in width and filled with thin fibrillar collagen fibers embedded in the amorphous substance. The lamellar cells contain rich microtubules and are characterized by the presence of caveolae on the surface plasma membrane. The terminal axon contains an abundance of mitochondria and small clear vesicles (20-50 nm in diameter). There are neurofilaments in the center of the axon terminal. Intermediate-type junctions are seen between the adjacent lamellar cells and between the axon and adjacent lamellae. The free nerve endings are found in the subepithelial regions, very close to the basal laminae of mucosal epithelium. They are surrounded by a thin cytoplasm of Schwann cells. Sometimes Schwann cell basal larinae become multilayered. Merkel cells are present within the basal layer of mucosal epithelium and contain characteristic electron-dense granules that are located almost exclusively at the side of cytoplasm in contact with axon terminals. Intermediate-type junctions are noted between axon terminals and Merkel cells.     

Vascular network in papillae of dog oral mucosa using corrosive resin casts with scanning electron microscopy

The purpose of this study was to undertake a three-dimensional analysis of the vascular network of the lamina propria in the gingiva, alveolar mucosa, buccal mucosa, palate, and lingual mucosa of the dog. Using the corrosive resin casting technique, casts of the vascular network were prepared and examined by scanning electron microscopy. In the oral mucosa, larger arteries in the submucosa divide into smaller branches that enter the lamina propria. These branches form one or more layers of vessels at the base of the papillae of the lamina propria, the so-called subpapillary vascular network. Here the vessels divide again and enter the papillae to form a subepithelial capillary network. The configuration of the capillary loops within each papilla of the lamina propria is determined by the shape of the papilla. The characteristic shape of the loops resembles a hairpin. The capillary loops in the lingual papillae are larger and more complex than capillary loops found elsewhere in the oral mucosa. The mucosa of the posterior portion of the hard palate, the soft palate, and the tongue contain many venous valves.     

Merkel cells, corpuscular nerve endings and free nerve endings in the mouse palatine mucosa express three subtypes of vesicular glutamate transporters

The hard palate of rodents is a mucous membrane covered by a keratinized epithelium that typically contains Merkel cell (MC)-neurite complexes. MCs have engendered considerable research activity because of their involvement in mechanoreception and possibly also Merkel cell carcinomas. MCs derive from the neural crest, differentiate under control of peripheral nerve factors, are enriched in large dense core vesicles, and secrete neuropeptides and other neuroactive molecules. Upon stimulation, MC-neurite complexes produce slowly adapting type I responses. Here we emphasize that the murine hard palate is a highly differentiated sensory region, as shown by intravital staining with a styryl dye and immunocytochemistry with antibodies to vesicular glutamate transporters (VGLUTs). The entire palate contained densities of sensory endings and MC-neurite complexes, that nearly paralleled in abundance the vibrissal pads. MCs were differentially distributed in the murine palate; clusters of MCs were most abundant in the antemolar and intermolar rugae, while individual MCs were particularly enriched in the rugae at the mid-portion of the palate and in the postrugal field. VGLUT1, VGLUT2 and VGLUT3 were expressed in MCs throughout, although immunostained MCs were most frequently encountered in intermolar than antemolar rugae. The same transporters were also present in corpuscular endings at the summit of the rugae and in intraepithelial free nerve endings throughout the palate. VGLUTs presumably load glutamate into large dense core vesicles in MCs and into small clear vesicles in corpuscular and free nerve endings. The data suggest that glutamate release, or co-release, is likely to represent an important functional aspect of palatine Merkel cells and neighboring corpuscular and free nerve endings.     

Sensory nerve endings in the anterior cruciate ligament (Lig. cruciatum anterius) of sheep

This study examines the structure of sensory nerve endings in the sheep anterior cruciate ligament (ACL). Three types of nerve endings are found: free nerve endings (FNE), Ruffini corpuscles, and lamellated corpuscles. The FNE (more than 100) are found subsynovially. The afferent nerve fibres are either thin myelinated axons (Aδ) or C fibres with diameters of 1–2 μm. FNE have been reported to function as thermoreceptors and polymodal nociceptors. In addition, FNE are also seen between fascicles of collagen fibres, often close to blood vessels. Part of this group may be efferent autonomic fibres controlling local blood flow. The corpuscles are seen subsynovially and between fascicles of connective tissue close to the attachment points of the ACL. A ligament contains about 20 Ruffini corpuscles, which are mainly located in the subsynovial connective tissue. They consist of cylinders formed from perineural cells surrounding the afferent myelinated axons (diameters 4–5 μm) with enlarged nerve terminals anchored between collagen fibres. These enter in bundles from the surrounding connective tissue at one open pole, pass through the length of the cylinder, and leave at the other pole. Functionally, Ruffini corpuscles have been described as slowly adapting stretch receptors. Lamellated corpuscles (usually between 5 and 15) are found in the subsynovial connective tissue. The afferent myelinated axon has a diameter of 4–6 μm, and the nerve terminal is located in the centre of numerous layers formed by lamellated terminal glial cells and by a perineural capsule. They are known to function as rapidly adapting pressure receptors. The most important function of the ACL is its mechanical function, but additional sensory functions must be considered triggering reflex mechanisms in case of extreme positioning or overload. Anat Rec 254:13–21, 1999. © 1999 Wiley‐Liss, Inc.     

Oral sensory papillae, chemo- and mechano-receptors, in the snake, Elaphe quadrivirgata. A light and electron microscopic study

The oral sensory papillae of the snake (Elaphe quadrivirgata), comprising a compound sensory system located along the tooth rows, were studied by light microscopy, immunohistochemistry for neuron specific enolase and S 100 protein, and scanning and transmission electron microscopy. Each sensory papilla exhibited a single taste bud and free nerve endings in the epithelium, and Meissner-like corpuscles, branched coiled terminals, and lamellated corpuscles in the connective tissue. The taste buds consisted of four types of cells; the type III cells, exclusively synapsing onto intragemmal nerves, were identified as gustatory in function. The gustatory cells included dense-cored and clear vesicles in the cytoplasm. These vesicles were accumulated both in the presynaptic and infranuclear regions, suggesting dual functions: the synaptocrine and paracrine/endocrine release of signal substances. The free nerve endings constantly contained mitochondria and frequent clear vesicles. The Meissner-like corpuscles were located in the uppermost zone of the connective tissue. These corpuscles consisted of nerve fibers and lamellar cells. The nerve fibers, rich in mitochondria, were folded and layered on each other. The branched coiled terminals were localized in the connective tissue along the side wall of the papillae. Nerve fibers, free from a Schwann-cell covering, swelled up to make terminals which accumulated mitochondria and glycogen particles. The lamellated corpuscles were associated with the nerve-fiber bundles in the connective tissue. Consisting of a central nerve axon and lamellar cells encircling it, these corpuscles resembled mammalian Vater-Pacini corpuscles, except that they lacked a capsule. These findings demonstrated that the snake sensory papilla represents one of the most specialized, compound sensory systems among vertebrates, which may play an important role in receiving chemical and mechanical information on prey.     

Sensory nerve endings in the beak skin of Japanese quail

Summary This study is concerned with the distribution and ultrastructure of sensory nerve endings in the beak skin of adult Japanese quail (Coturnix coturnix japonica). The following nerve endings were found: free nerve endings, clusters of dermal Merkel nerve endings, Herbst corpuscles and Ruffmi corpuscles. The latter were found only in the dermis of the tip of the upper beak. The remaining endings were present in the skin of all areas of upper and lower beak. Free nerve endings were supplied by either thin myelinated axons or unmyelinated C-fibers and were localized in the dermis close to the basal layer of the epidermis. Merkel cells formed clusters (up to 50) localized below and between the epidermal cones of the beak skin. Disc-shaped thickenings of nerve endings were squeezed between individual Merkel cells. Small Herbst corpuscles were found in the dermis close to the epidermal cones of the beak skin. Large Herbst corpuscles occurred in deep layers of the dermis. The Ruffmi corpuscles were cylindrical in shape (80 m × 400 m) and arranged in groups of up to ten corpuscles. Each corpuscle was surrounded by an incomplete fibrous capsule.     

Trigeminal nerve endings in gingiva,junctional epithelium and periodontal ligament of rat molars as demonstrated by autoradiography

Tritiated-L-proline was injected into the right Gasserian ganglion of mature rats for incorporation into proteins being carried by rapid axonal transport to nerve endings. The distribution of the nerve endings in molar gingivae and periodontium was subsequently mapped in serial sections by autoradiography. We found that sensory nerve terminals are most prominent in two regions of the free gingiva: (1) In the junctional epithelium there is a rich innervation of the basal epithelial layer with many endings penetrating several cell layers. (2) In the crestal epithelium arborized endings are present, especially on the marginal side of the crest. In the attached gingiva a few terminals are found in the epithelium with more in the lamina propria; the latter appear to be encapsulated. The periodontal ligament is only moderately labeled with silver grains located over nerve bundles, over nerves associated with blood vessels, and over a few apparent endings in the apical region. In the cementum no labeled endings are seen. Labeling of Gasserian cell bodies primarily reveals specific intra-epithelial nerve endings in gingival crest and junctional epithelium. The absence of major labeling of the periodontal ligament supports the view that many nerves in that region are derived from cell bodies in the mesencephalic nucleus.     

Microvascular architecture of the hard palatine mucosa in the rabbit

SEM studies on the microvascular architecture of the hard palatine mucosa, especially the transverse palatine plicae, and the morphological relations between the microvasculature and layers of the hard palate mucosa of the rabbit, were carried out by the acryl plastic injection method. The findings were compared with those obtained previously in the cat and Japanese monkey. Morphological differences and similarities between the papillae in the lamina propria and the capillary loops in the papillae were elucidated by SEM. A boneless area was found in the hard palate since the palatine fissures occupied a large area between the diastemata. The transverse palatine plicae numbered 14-16 symmetrically in the hard palate, and were more developed than those in the cat and Japanese monkey. In sagittal sections of the hard palate, the transverse palatine plicae were observed to be serrated, since they were located close to each other with small narrow interplical regions. The plical branches were usually derived from the major and minor hard palatine arteries, and formed the primary arterial network in the submucous layer of the hard palate. Twigs diverging from this network formed the second arterial plexus in the lamina propria, and furthermore, a subepithelial capillary network was formed immediately beneath the epithelium. From this network, capillary loops sprouted into papillae. Similarities were found between the papillae and capillary loops with locational differences. The descending crus of the capillary loop drained into the venous site of the subepithelial capillary network which flowed into the primary venous plexus in the lamina propria, which finally poured into the second venous plexus in the submucous layer. This plexus was termed the palatine venous plexus, and was especially well-developed in the area covering the palatine fissures. The capillary loops in the plica displayed characteristic features according to the portions within it and the interplical regions.     

Microvascular patterns of the hard palatine mucosa in the Japanese monkey (Macaca fuscata)

Detailed investigations were made of the microvasculature of the mucous membrane, especially the transverse palatine plicae, of the hard palate of the Japanese monkey (Macaca fuscata) utilizing the plastic injection method. The microvascular patterns obtained were compared with those of the cat and other mammals. The incisive papilla was located at the anterior end of the median line of the hard palate, and seven or eight transverse palatine plicae were observed symmetrically from this papilla posteriorly at similar intervals. Each plica arched bilaterally in a wide M. The heights of the plicae decreased gradually at their lateral ends. The whole palate was supplied by two arteries. The minor palatine artery supplied the soft palate and the major palatine passed forwards to supply the hard palate, sending off numerous, medical and lateral branches. The plical branches diverging from both these branches formed a primary arterial network (submucous arterial network), and arterioles diverging superiorly from this network formed a second arterial network (arterial network in the lamina propria). Fine twigs diverging from the latter network formed a subepithelial capillary network immediately beneath the epithelium. Capillary loops sprouted out of the above network in the lamina propria. The descending crus of each loop drained via the subepithelial capillary network of the venous side into a venous network located in the same layer as the arterial network. These vessels finally drained into the submucous venous network (palatine venous plexus). In conclusion, the transverse palatine plicae in M. fuscata were formed from a thickening or eminence of the lamina propria, as opposed to the submucous tissue in the cat. Accordingly, the presence of such submucous tissue has been not observed in M. fuscata except in a limited area of the hard palate. The microvascular patterns of the hard palate of M. fuscata were similar to those of the cat.     

Fine structure of Eimer's organ in the coast mole (Scapanus orarius)

Eimer's organ is a small, densely innervated sensory structure found on the glabrous rhinarium of most talpid moles. This structure consists of an epidermal papilla containing a central circular column of cells associated with intraepidermal free nerve endings, Merkel cell neurite complexes, and lamellated corpuscles. The free nerve endings within the central cell column form a ring invested in the margins of the column, surrounding 1–2 fibers that pass through the center of the column. A group of small‐diameter nociceptive free nerve endings that are immunoreactive for substance P surrounds this central ring of larger‐diameter free nerve endings. Transmission electron microscopy revealed a high concentration of tonofibrils in the epidermal cells of the central column, suggesting they are more rigid than the surrounding keratinocytes and may play a mechanical role in transducing stimuli to the different receptor terminals. The intraepidermal free nerve endings within the central column begin to degrade 15 μm from the base of the stratum corneum and do not appear to be active within the keratinized outer layer. The peripheral free nerve endings are structurally distinct from their counterparts in the central column and immunocytochemical double labeling with myelin basic protein and substance P indicates these afferents are unmyelinated. Merkel cell‐neurite complexes and lamellated corpuscles are similar in morphology to those found in a range of other mammalian skin. Anat Rec, 2007. © 2007 Wiley‐Liss, Inc.     

Afferent nerve endings in the urinary bladder of the cat

In five cats, sacral dorsal rhizotomies were performed, alone or in conjunction with sympathetic nerve transections. Urinary bladders, collected 7, 10, or 30 days following the nerve transections, were sectioned and stained by the Holmes silver nitrate and the Nauta and Gygax methods and examined under the light microscope. Degenerative changes occurred in bladders of all the cats permitting an assessment of the appearance and distribution of vesical sensory endings. Degenerated myelinated axons and nerve terminals were found bilaterally in bladders, although they were more numerous ipsilateral to the transections. Within the muscle coat, degenerated endings were found in the perifascicular connective tissue, and less frequently, on the surface of muscle fascicles; endings were not seen among the muscle cells within a fascicle. Sensory endings were identified in the subserosa and lamina propria but not in transitional epithelium. Except for an occasional Paccinian corpuscle, encapsulated endings were not found. Afferent endings in the bladder appeared to be non-encapsulated and without terminal fiber modifications.     

Distinct types of encapsulated sensory corpuscles in the oral mucosa of the dog: immunohistochemical and electron microscopic studies

The types, structure, and distribution of encapsulated sensory endings that have lamellar investments in the oral mucosa and vermilion border of the lip of adult dogs were studied by light and electron microscopy. Immunohistochemistry for cholinesterase was used to identify the corpuscules by light microscopy. Two different types of corpuscular end-organs containing definite inner cores were distinguished. One was a typical, simple corpuscle, which contains only one, but sometimes two, inner cores composed of densely piled cytoplasmic lamellae surrounding a central axon terminal. The other type was characterized by the coexistence of convoluted inner cores, arborized free endings, and thin nerve bundles within a perineural capsule; we term this type "compound corpuscle." The ultrastructure of the inner cores in compound corpuscles was similar to that of mature, simple corpuscles. The arborized free endings in the compound corpuscles usually contained an accumulation of mitochondria and small clear vesicles. The compound corpuscles were frequently encountered in the vermilion border of the lip and in the labial and buccal mucosae but were rare in the masticatory mucosa of the gingiva and hard palate. From the results, it was concluded that the compound corpuscle is a distinct type of the sensory end-organ containing inner cores.     

Microanatomy of the major airway mucosa of the bowhead whale, Balaena mysticetus

In the bowhead whale, Balaena mysticetus, the mucosa of the major airways from the blowholes through the rostral portion of the larynx is lined with parakeratotic, pigmented, stratified squamous epithelium. Scattered enlarged connective tissue papillae of the lamina propria of the nasal vestibules and the palatopharyngeal sphincter contain encapsulated nerve endings. Abundant papillae in the mucosa covering the epiglottic and arytenoid cartilages contain similar nerve endings. The remainder of the laryngeal cavity and laryngeal sac is lined by a variably pigmented, stratified squamous epithelium, which is not keratinized. At the laryngotracheal junction the lining changes to ciliated pseudostratified columnar epithelium which continues through the trachea and principal bronchi. Scanning electron microscopy (SEM) indicates that this epithelium is typically mammalian, with approximately half of the surface cells bearing cilia and slender microvilli. The remaining cells are mucus producing and have thicker microvilli. The valvular mass regulating the external nares consists of irregular, dense white fibrous connective tissue with numerous adipose cells and is penetrated by skeletal muscle cords ranging from 2-4 mm in diameter. The septal mass between the blowholes is composed of irregular, dense white fibrous connective tissue containing large tendinous bundles, clusters of adipose cells, and several large arteries and thick-walled veins. The lamina propria of the nasal vestibules is irregular, dense white fibrous connective tissue. That of the larynx is not as dense and contains proportionately more elastic fibers. The laryngeal sac does not contain elastic laminae, but does have a tunica muscularis of skeletal muscle bundles. Within the trachea and principal bronchi, the lamina propria possesses laminae of longitudinally oriented elastic fibers and simple, branched tubuloalveolar mucous glands. The nasal, laryngeal, tracheal, and bronchial cartilages are hyaline with vascular channels.     

Distribution of sensory receptors in joints of the upper cervical column in the laboratory marsupial monodelphis domestica.

In order to investigate the sensory innervation, the upper cervical spine of a small laboratory marsupial (monodelphis domestica) was examined with serial section light microscopy and re-embedding of selected sections for electron microscopy. Large numbers of free nerve endings supplied by A delta- and C-fibres were found in the longitudinal ligaments and facet joint capsules. Electron microscopically, areas of direct contact between axon and collagen fibres of the surrounding connective tissue separated only by the basal lamina were observed. Such structural adaptations suggest mechanoreceptive or polymodal nociceptive functions. In addition, about 100 small lamellated corpuscles were found in the longitudinal ligaments mainly concentrated around the first intervertebral disk. Electron microscopy shows finger-like processes extending from the axon terminal into the inner core lamellae. These are the likely sites of the mechanoelectric transduction process. Smaller numbers of lamellated corpuscles were seen in the lower intervertebral disks and facet joint capsules. Lamellated corpuscles are known to function as rapidly adapting mechanoreceptors supplementing information supplied by muscle spindles to the CNS about position and movement of the cervical spine.     

Comparative anatomical and neurohistological observations on the tongue of Japanese pika (Ochotona hyperborea yezoensis,kishida)

The tongue of the Japanese pika was investigated using the silver impregnation method. On the dorsum, three vallate papillae, arranged in a row transversely, and foliate papillae with 12–13 clefts were observed. The papillae are both covered with an upper thickened epithelium. The abundant nerve fibers are widely distributed in the subpapillary layer of the lamina propria to form the subpapillary nerve plexus, which is composed of non-myelinated and thick myelinated fibers, and ganglion cells. The taste buds, of an embryonic type with an indefinite border, are located as a mass in both walls of the papillae symmetrically, closely associated with a small number of the fine fibers from the subpapillary plexus. They are large in size and penetrate into the subgemmal connective tissue. Their aspect suggests a peculiar receptive apparatus surrounding the orifice of the serous gland-ducts. In the papilla regions the serous glands are plentiful deep in the muscles and their ducts open into the bottom of the trench and furrow. The dorsum is densely packed only with the filiform papillae which are covered with highly cornified, thickened stratified squamous epithelium and poor in nerve supply, but the smooth inferior surface is well supplied with sensory nerves ending free and is furnished with many taste buds. No apical glands are present. The tongue contains many ganglion cells alongside the nerve fiber bundles running toward the apex.