Okajimas Folia Anat. Jpn., 63 (4) 179-192, October 1986

Scanning Electron Microscopic Study on the Plicae Palatinae Transversae and their Microvascular Patterns in the Cat

By

Isumi TODA

Department of Anatomy, Osaka Dental University 1-47 Kyobashi, Higashi-ku, Osaka 540, Japan (Director: Prof. Y. Ohta) (with 1 text-figure and 14 figures in 3 plates)

-Received for Publication, June 25, 1986-

Key Words: Transverse palatine ridge, Hard palate, SEM, Plastic injection, Cat

Summary: The microvasculature in the plicae palatinae transversae of the hard palate of the cat was investigated by means of the acryl plastic injection method under a scanning electron microscope (SEM). On the hard palate of the cat, seven or eight transverse palatine ridges arching forwards were observed. Small digitiform processes were located on the top line of each ridge, and anterior and posterior conical processes were present on both the anterior and posterior slopes of each ridge. The lateral ends of each ridge were observed as simple forms in which these processes disappeared. The blood supply of the ridges came from the lateral and medial branches of the a. pala- tina dura major. These branches formed a primary arterial network in the submucosa super- ficial to the palatine venous plexus. Small twigs were derived from this network to form a secondary arterial network in the lamina propria. Further, from this network formed a subepithelial network immediately beneath the epithelium. From this net work, capillary loops sprouted into the papillae of the lamina propria. Blood from the subepithelial capillary network drained into the primary venous network in the lamina propria, from which drained into the superficial layer of the palatine venous plexus in the submucosa, and then into its deeper layer. The entire microvascular pattern of the hard palate of the cat was thus investigated and used to assess and confirm the lamina-formation of the palatine mucosa. Regions of thickening such as the transverse palatine ridges of the cat were not formed by thickening of the lamina propria, but by the submucous tissue including the vascular complex.

General pictures of the fine vasculature mucosae, the hard palate is covered with an of the mucosae of many organs have been immovable mucosa, in which the border obtained by various methods. In particular, between the lamina propria and the sub- Tsudomi (1963) investigated that of the mucosa is not obvious, and submucosal digestive mucosae in relation to their histo- tissue is not present. logical structure. However, the structures On the hard palate of the cat, the plicae of the oral mucosa differ from those of palatinae transversae, which are peculiar to other digestive mucosae, such as of the eso- this species, are located in a regular fashion. phagus, stomach, etc. Among the oral The blood supply to the palate of the cat

179 1 80 I. Toda

has been described by Hiirlimann (1913), scanning electron microscope (JSM-T300, Davis et al. (1943), Miyazaki (1960) and JEOL, Tokyo). Sawa (1961), although they did not eluci- 2) Histologicalslides of the injected materials date its microvasculature at the SEM level. Using two other cats, acryl plastic was The present paper deals three-dimension- injected by the above procedures. The in- ally withthe microvasculature of the pala- jected palatine tissues were then fixed in tine ridges in microcasts, in relation to the . 10% formalin, embedded in celloidin and surrounding layers of the mucosa in histo- cut for serial sections of 10 pm thick. Every logical slides of injected materials. By fifth slide was stained with hematoxylin. elucidating the laminar structures of the These slides were employed to observe re- microvascular patterns of the hard palate , lations between the vascularpatterns and the it should be possible to confirm the lamina- surroundingstructures. formation of the histological structures . 3) SEM specimens of the palatine mucous surface Materials and Methods Two cats were perfused from the carotid with 2.5% glutaraldehyde. The Twenty adult cats were employed for this material from one cat was post-fixed with study.They were bled to deathafterinject- 2% osmic acid, treated in the critical point ing heparin intravenously. The following dryer and coated with gold for SEM, and specimens were employed. was mainly employed for comparison with 1) Casts of the vascular patterns of the the plaster model. The other material was palatine region prepared for serial sections of 15 Am thick Acryl plastic was injected into the caro- after celloidin-embedding,and stained with tid arteries of ten cats by means of the hem atoxylin -e osin . plastic injection method (Taniguchi, Ohta et al., 1952, 1955). Plaster models were Findings made by taking an alginate impression of the palatine mucous surface. The injected I. Macroscopic features of the plicae pala- palatine tissues were then treated with tinae transversae sodium hypochlorite solution to remove the On the hard palate of the cat, seven soft tissues and so obtain microcasts of their or eight plicae (ridges) palatinae transversae vascular patterns. arched anteriorly (Figs. 2, 3), and each end Using another six cats, red colored plastic of them curved posterolaterally. They were was injected into the ascending and mostly observed as symmetrical arches, blue colored plastic into the vena cava although they rarely branched at their ends superior. The injected palatine region was or adhered with each other (Fig. 4). treated with 10% sodium hydroxide in order The anterior slope of each ridge was longer to obtain casts of its vascular pattern. The than the posterior slope, so that the post- two-colored casts were used for exami- erior slope was somewhat steeper. In the nation of the differences between the arterial median one third of each ridge, small digiti- and venous elements. form processes (about 500 gm in height, All these casts were observed primarily and about 300 Am in basal diameter) were under a stereoscopic dissection microscope observed along its top line. These processes to cut down the microcasts in the palatine were more distinct near the median line, region. The materials dissected out were but became smallernear the end of the ridge coated with gold for examination under a (Figs. 2, 3). On the anterior and posterior

SEM Study on the Plicae Palatinae Transversae in the Cat 181 slopes, anterior and posterior conical pro- in the posterolateral region was defective cesses (about 700 pm in height, and about and the superficial layer was in direct con- 500 ,um in basal diameter) (indicated as tact with the periosteum (Fig. 6). small triangular processes by Iwaku (1976)), The whole venous plexus was composed numbering 14 — 20, were located regularly of venous vesselsrunning sagittally. Venous parallel to the ridge. These two kinds of vesselscommunicating between the plexuses processes became smaller laterally and dis- of both sides were observed in the super- appeared at the lateral end of the ridge ficial layer, much more especially in the (Figs. 2, 3). ridges. No palatine gland was observed in the hard palate of the cat. II. Histological features of the plicae pala- tinae transversae III. Vascular patterns of the plicae pala- The stratified squamous epithelium cover- tinae transversae ing the hard palate was similar in thickness 1. Arterial system all other with thin keratinizations. The 1) General aspect in the hard palate (Fig. 1) lamina propria was also similar in thickness The a. palatina dura major (Sawa, 1961) except for a slightly thicker area on the ran on the bone surface in the posterior ridges. Both small digitiform and conical third of the hard palate and superficial to processeswere formed by protrusions of the the palatine venous plexus in the anterior lamina propria itself. The papillae on the two thirds, and en route gave rise to the ridge and hese processes were highest on medial and lateral branches (Sawa) (Fig. 7). the anterior side and lowest on the posterior Each of these branches ran medially or side with a smaller number (Fig. 5), and laterally in a layer superficial to the sub- those between the ridges were usually low. mucous tissue and the venous plexus, imme- They becamelower at the lateral end of each diately beneath the palatine ridge. They ridge with disappearance of the processes formed the submucous arterial network, that is, the primary arterial network. This (Fig. 6). The submucous layer was similarin thick- was formed directly in contact with the ness to the lamina propria. It can be said to periosteum in the posterolateral region of the hard palate due to the lack of the divide into superficial and deep layers. The superficial layer was composed of con- venous plexus. Part of the primary network siderably dense connective tissues including in the anterior one third of the hard palate the palatine venous plexus formed by finer was developed into the incisive arterial venous vessels. This layer became thicker in network (Sawa) (Fig. 7) since the medial and lateral branches were usually so thick proportion to the height of the ridge except in both processes (Fig. 5). Almost all of the that they were often similar to the a. pala- deep layer was occupied with the palatine tina dura major. venous plexus formed by thick venous vessels From the primary, submucous arterial and directly lined by the periosteum (Fig. 5). network, small twigs were derived towards This layer was mostly similar in thickness the epithelial surface. They ramified tan- all over the hard palate. The venous plexus gential to the surface between the sub- in this layer was observed only beneath the mucosa and lamina propria, and formed an ridges in the anterior half of the hard palate, incomplete, arterial network in the lamina and only in the median regionof its posterior propria, that is, the secondary arterial half, not in the posterolateral regionsof both network (Fig. 8). sides (Fig. 6). Accordingly, the deep layer 2) Vascular patterns in the palatine ridges 182 I. Toda

Fig. I. Schematic illustration of the microvascular patterns of the transverse palatine ridge in sagittal section. For abbreviations, see page 10 . and the processes (Fig. 1) derivations of the arterioles (Fig. 11). Such The medial and lateral branches running arterioles directed to the top of the ridge along and immediately beneath each ridge or process were distributed to the ridge, mentioned above may be called the palatine the anterior and posterior conical processes, plical branches (Fig. 7). by forming the subepithelial capillary The plical branch gave rise to twigs to- network (Fig. 11). wards the top line of the ridge as well as Capillary loops sprouted from this net- twigs to the anterior and posterior conical work into the papillae of the ridge and processes anteriorly and posteriorly. Actually process. Usually each of the loops was the former twig was derived from the primary observed as a single form and its descending arterial network horizontally along the crus drained into the venous-sidecapillary course of the ridge towards its top line network (Fig. 12). Accompaniedby arterio- and gave off an into each small les, they confluenced with each other to digitiform process (Fig. 9). The latter twig drain into the venules which formed the gave off arterioles into each process ana- venous network in the lamina propria, stomosing with adjacent ones (Figs. 10, 11). that is, the primary venous network (Fig. These twigs gave rise to arterioles just 11). The height of the capillary loops de- at the height of the secondary network, but creased near the lateral end of the ridge never communicated with it. Accordingly, (Fig. 13). this network discontinued immediately be- 3) Vascular patterns in areas between the neath the ridge and processes because of the palatine ridges (Fig. 1) SEM Study on the Plicae Palatinae Transversae in the Cat 183 From the secondary arterial network mucosa protruded according to the form of mentioned above, arterioles were derived the ridge (Fig. 8). Finally, the venous and formed the subepithelial capillary net- plexus drained into the deep facial . work (Fig. 14). This network gave rise to Deeper to the plexus, a coarse, periosteal capillary loops into the papillae. The des- vascular network was observed in the shape cending crus of each loop drained into the of a capillary network (Fig. 15). venous network in the lamina propria via the venous-sidecapillary network (Fig. 14). Discussion The height of this loop was broadly similar to that of the papillae. Most of the loops The blood supply of the palate of the cat were observed in the shape of a single hair- has been investigatedby Hiirlimann (1913), pin which consisted of the ascending and Davis et al. (1943), Miyazaki (1960) and descending crura. Sometimes, the loop had Sawa (1961). However, they did not des- one ascending and two descending crura cribe the microvascular patterns of the or another loop between both cura (Fig. 14). palatine mucosa and ridges. Suzuki (1964) examined the fine vascular patterns of the 2. Venous system (Fig. 1) palatine mucosa in the human adult and Venules draining away from the subepi- fetus by means of the indian-ink injection thelial capillary network did not descend method. Sayo (1985) demonstrated three in company with arterioles at their begin- vascular layers, viz, the lamina propria, nings, but gradually came to be in company with them. The venules drained into the the submucosal and the subperiosteal, in the palatine mucosa of the dog. However,he venous network in the lamina propria, that is, the primary venous network (Fig. 11). did not clearly specify the differences be- This network was formed incompletely, but tween the arterial and venous components was located close and superficial to the in each vascularlayer. The lamina-formation secondary arterial network (Fig. 11), from of the vascular patterns demonstrated by which venous branches drained into the Sayo was not based on a three-dimensional secondary, fine venous plexus located approach to the vascular networks them- close to and immediately beneath the pri- selves, but followed only the histological mary arterial network in the superficial lamina-formation. layer of the submucosa (Fig. 8). This plexus The present author's aim was to elucidate drained into the palatine venous plexus the lamina-formationof the vascular patterns on the hard palatine mucosa in relation to (Fig. 8), which was especially well develop- ed in the anterior half of the hard palate. It its histological structures. Only in the areas was composed of three to four layered, where the medial and lateral branches of thick venous vessels (Fig. 8). The plexus, the a. palatina dura major (Sawa 1961) and however, was located only in the median the palatine venous plexus were located, one third of the posterior half of the hard was the primary or the submucous arterial network, formed superficial to the plexus. palate and was composed of one or two layered vessels, running in a sagittal direc- In particular, in an area anterior to the tion. The component venous vessels were line between the canines of both sides, this thicker with strong meandering in the deep network was well developed in the shape of the incisive arterial network as named by layer of the submucosa (Fig. 8). Beneath the ridge, the secondary venous plexus Sawa. This network can be said to be the located in the superficial layer of the sub- primary arterial network, judging from its 184 I. Toda

-although it is not found in the hard palate component vessels and location. From the , primary arterial network, many small twigs would be situated between the lamina sprouted upwards and spread tangential to propria and the submucosa, or deeper to the the mucosal surface and formed the second- secondary arterial and primary venous ary arterial network in the lamina propria, networks. Accordingly, the histological which expanded bidimensionally in the lamina-formation of the lamina propria border between the lamina propria and sub- and the submucosa can be explained if mucosa. The secondary network, however, the microvascular patterns in both layers was seen to have the shape of an extremely are elucidated in detail. On the basis of the incomplete network in comparison with present study, it can be said that the trans- the other arterial networks. This network verse palatine ridges themselves are not discontinued immediately beneath each formed by thickening of the lamina pro- palatine ridge. This is one reason why pria, but actually by thickening of their the small twigs sprouting from the primary submucosa including the vascular complex. arterial network spread towards the top line of the ridge three-dimensionally.Arteri- Acknowledgements oles arising from the secondary arterial net- work arborized in the lamina propria and The author wishes to express his sincere extended up to the height immediately gratitude to Professor Y. Ohta for critically beneath the epithelium, where the sub- reading the manuscript, and to Assistant epithelial capillary network was formed, Professor T. Tokioka and all staff members and gave rise to capillary loops in the shape of the Department of Anatomy for their in- of a hairpin into the papillae. Venules from valuable assistance. the capillary network were deeply directed Part of this work was supported by a down to a position imme&ately beneath grant-in-aid from The Yamazaki Foundation the secondary arterial network, where they for Dental Research in 1985. formed the primary venous network in the lamina propria. Through this network, the blood drained into the superficial layer of References the secondary venous plexus in the sub- 1) Davis, D.D. and H.E. Story: The carotid circu- mucosa, which was characteristic in the cat lation in the domestic cat. Zool. Series, Field palate, and was then transferred to its deeper Mus. of Nat. History, 28: 27-29, 1943. layer. 2) Hiirlimann, R.: Die arteriellen Kopfgefdsse Concerning the vascular pattern of the der Katze. Intern. Mschr. Anat., 29: 415, hard palate of the cat, the present author 428-429, 1913. 3) Iwaku, F.: The morphological study of the attempted to analyze it in a similar manner transverse palatine ridges in mammals. to the general vasculature of the digestive NIIGATA Dent. J., 6: 103-143, 1976 (in mucosa described by Tsudomi (1963). The Japanese). palatine venous plexus and the primary 4) Miyazaki, K.: Untersuchung iiber den Blut- versorgungsplan des Oberkiefers von Katze. arterial network were formed in the sub- J. KUR. M.A., 23: 3087-3107, 1960 (in mucous tissue, as well as the secondary Japanese). arterial network and the primary venous 5) Sawa, H.: Cubical anatomy of several ducts network between the submucosa and the and vessels by injection method of acrylic lamina propria. Judging from this arrange- resin. X. Arterial distribution of the palate in some mammals. Okajimas Folia Anat. ment, the lamina muscularis mucosae, Jpn., 37: 49-92, 1961. SEM Study on the Plicae Palatinae Transversae in the Cat 185

6) Sayo, Y.: A scanning electron microscope resin. Okajimas Folia Anat. Jpn.24: 259-267, study on vascular architecture of dog palate 1952. mucosa using corrosion casts. KANAGAWA 9) Taniguchi, Y., Y. Ohta, S. Tajiri, H. Okano SHIGAKU, 20: 167-191, 1985 (in Japanese). and H. Hanai: Supplement to new improved 7) Suzuki, K.: The study of the fine vasculature method for injection of acrylic resin. Okajimas of the gingival and palatine mucosae. SHIKWA Folia Anat. Jpn., 27: 401-406, 1955. GAKUHO, 64: 705-725, 1964 (in Japanese). 10) Tsudomi, N.: Microangiogram of fine vessels 8) Taniguchi, Y., Y. Ohta and S. Tajiri: New of the digestive canal in the human fetus. Unproved method for injection of acrylic SHIKWA GAKUHO, 63: 681-704, 1963 (in Japanese).

Abbreviations for Figures cn : Subepithelial capillary network C : Anterior and posterior conical processes pa : Primary arterial network LP : Lamina propria pv : Primary venous network SM : Submucosa sa : Secondary arterial network T : Top line of ridge v : Palatine venous plexus .11I^ Direction of snout B: Bones of the hard palate 186 I. Toda

Explanation of Figures

Plate I

Figs.2 and 3. Surfaceview of the hard palate of the cat. In Fig. 2, seven transverse palatine ridges are seen in this specimen.The small digitiformprocesses ( f) are located on the median one third of the top line of eachridge, and the anterior and posteriorconical processes(4.) on the anterior and posterior slopesof each ridge,respectively. These processesare not observ- ed near the lateral end of the ridge. X 2.4. In Fig. 3, the vascular casts of the whole palatine mucosa present similar surface features to those in Fig. 2. X 2.6.

Fig. 4 (inset). Plaster model of the hard palatine surface after injection into the blood vessels. In this case, two ridges on the left side can be seen to adhere to one another (t). X 1.4.

Fig. S. Midsagittal section through the ridges. Fig. 6. Sagittal section through the lateral end of the ridge. In Fig. 5, the papillae in the ridge are higher on its anterior slope and lower on its posterior slope. The lamina propria of both slopes are similar in thickness. The palatine venous plexus is composed of several layered vessels, of which the superficial ones are more distinct on the ridge and the deep ones are similar all over. X8.9. In Fig. 6, the small digitiform and conical processes are not observed. The ridge becomes simpler with lower papillae. The superficial layer of the submucosa is clearly seen and contacts directly with the perio- steum. Its deep layer and the palatine venous plexus are not seen. The border between the lamina propria and submucosa is indicated by the dotted line. X 14.1.

Fig. 7. Positional relations between the primary arterial network (light) and the palatine venous plexus (dark). The a. palatina dura major (*) passes forwards in the layer superficial to the venous plexus, giving rise to the medial (4) and lateral (t) branches, that is, the palatine plical branches. They run medially or laterally along the ridges, respectively. in the anterior area of the hard palate, they form the incisive arterial network (dotted lines). X2.9. SEM Study on the Plicae Palatinae Transversae in the Cat 187 Plate I 188 I. Toda

Plate II

Fig.8. Midsagittalsection of the ridge. Smallarterial twigs arise from the primary arterial network and form an incomplete,secondary arterialnetwork (J) tangentiallyin a positionbetween the laminapropria and submucosa.This network is moredistinct in the areabetween ridges CO . Venousvessels drain from the primaryvenous network into the secondary network, that is, the palatine venous plexus, which is formed by strongly meandering venous vessels in several layers. The component vessels in the superficial layer are not thick and form somewhat thicker layers in the ridges, but those in the deeper layer are always thick. X 22.7.

Fig. 9. Posterior view of the ridge, especially showing three small digitiform processes in its longi- tudinal section. Small twigs (0) arise from the primary arterial network along the ridge towards its top line. Arterioles (A) sprout from these twigs into each small digitiform process ( t). X 89.7.

Figs. 10 and 11. Frontal (Fig. 10) and sagittal (Fig. 11) sections of the anterior conical processes. Small twigs of the plical branch form the secondary arterial network anastomosing () with adjacent ones, although the network ends immediately beneath the ridge and process. Arterioles (-4) arise from the network to supply the process, forming the subepithelial capillary network, from which capillary loops sprout into papillae (cf. Fig. 12). Venules (+-) from the capillary netwrok drain into the primary venous network in company with arterioles. This venous network is usually incomplete in contact and superficial to the secondary arterial network. X 38, X 33.7, respectively. SEM Study on the Plicae Palatinae Transversae in the Cat 189 Plate II 190 I. Toda

Plate III

Fig. 12. Subepithelial capillary network and capillary loops in the ridge. The capillary loops are usually high and mostly in the shape of a hairpin (t). X75.5.

Fig. 13. Sagittal section through the lateral one third of the ridge. Both small digitiform and conical processes are absent. This portion of each ridge is seen as a simple feature with lower capillary loops (cf. Fig. 8). X 39.1.

Fig. 14. Secondary arterial network and subepithelial capillary network in the lamina propria in areas between the ridges. Arterioles (—>. ) arising from the secondary arterial network form the subepithelial capillary network, from which capillary loops sprout. They are low mostly in the shape of a hairpin ( t ). Blood from the subepi- thelial capillary network drains into the primary venous network through venules (<—). X 172.6.

Fig. 15. Superior (nasal) view of the palatine venous plexus, after removal of the bone structure. The periosteal capillary network (t) is observed in close contact with the palatine venous plexus. X55.7. SEM Study on the Plicae Palatinae Transversae in the Cat 191 Plate III