Color Atlas of Xenopus laevis Histology
Book: Color Atlas of Xenopus laevis Histology
Authors: Allan F. Wiechmann & Celeste R. Wirsig-Wiechmann
ISBN: 1-4020-7375-5
Copyright © 2003 Kluwer Academic Publishers.
This page contains select figures with captions of stained adult Xenopus laevis histological sections of specific tissues.
The chapters of the book are:
1. Basic Tissues
2. Cardiovascular System
3. Basic Lymphatic Organs
4. Digestive Organs
5. Respiratory System
6. Urinary System
7. Endocrine Organs
8. Reproductive Organs
9. Integument
10. Cranial Structures
Select images and captions reproduced with kind permission from Springer Science & Business Media B.V.
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Chapter 1: Basic Tissues - examples of cellular structures within various tissues
Figure 1.
Simple squamous epithelium. Simple squamous epithelium consists of a single layer of flattened cells that typically line a lumen, body cavity or surface. A. Simple squamous epithelium lining the outer surface of the oocytes. B. Simple squamous epithelium lining the outer surface of the colon. The epithelium and underlying connective tissue make up the serosa. Directly underlying the serosa is smooth muscle in cross-section. At the lowest part of the figure is smooth muscle in longitudinal or oblique orientation. Between the two muscle layers is a neuron (*), which is part of the post-ganglionic parasympathetic plexus called Auerbach's plexus, or the myenteric plexus, which innervates the smooth muscle cells. XB-IMG-158223
Figure 3.
Simple cuboidal epithelium. Simple cuboidal epithelium cells line the inner surface of ducts in the pancreas. The epithelium of the larger duct could also be classified as low columnar epithelium. Loose connective tissue surrounds the ducts. XB-IMG-158224
Figure 4.
Simple columnar epithelium. A. Simple columnar epithelium lines the lumen of the gall bladder. The columnar cells are taller than they are wide. The epithelium is observed in a longitudinal orientation. Loose connective tissue underlies the epithelium, as it does in all organs. B. Simple columnar epithelial cells of the gall bladder shown in oblique section. XB-IMG-158225
Figure 5.
Stratified squamous keratinized epithelium. The outer layer of the skin, especially in adult Xenopus, is also referred to as 'stratified squamous epithelium'. It can be keratinized or non-keratinized. A. Low magnification of the stratified squamous keratinized epithelium (arrow) of the epidermis of the skin. Note the presence of exocrine gland and dense irregular connective tissue in the underlying dermis. B. High magnification of the epidermis. Arrowheads indicate the superficial layer of the squamous epithelium. There is a thin layer of protective keratin above the cells . Note the thick basement membrane (pink) indicated by arrow on the basal surface of the epithelium, which separates the epithelium from the underlying loose connective tissue. The dark brown cells are pigment cells. XB-IMG-158226
Figure 6.
Stratified squamous non-keratinized epithelium. The simple stratified non-keratinized epithelium (arrow) of the epidermis of the cornea. The short arrow indicates the superficial layer of the squamous epithelium. Note the basement membrane (long arrow) separates the epithelium from the underlying connective tissue. XB-IMG-158228
Figure 9.
Pseudostratified columnar epithelium. An example of pseudostratisfied columnar epithelium is the neural olfactory epithelium in the nasal cavity. In this example, the sensory cilia on the apical surface are obscured by a layer of mucous (*). The columnar epithelial cells all contact a basement membrane. XB-IMG-158235
Figure 15.
Hyaline cartilage. A. Low magnification image of the hyaline cartilage that provides structural support for the trachea. Note that the cartilage is completely surrounded by a dense connective tissue perichondrium, which is one source of new chondrocytes. B. High magnification of the trachea showing lacunar spaces occupied by chondrocytes. Chondrocytes are not well-preserved during fixation, but the nuclei can be discerned. Isogenic groups are clusters of daughter chondrocytes that have dived, and will produce additional basophilic matrix resulting in interstitial growth. XB-IMG-158229
Figure 22.
Osteoblasts and osteoclasts. A. Osteoblasts line the bone surface, and produce and calcify the bone matrix (osteoid). they are basophilic cuboidal -like cells. After secreting osteoid, they eventually become entrapped in the bone matrix that they produced and become osteocytes (*). B. Osteoclasts resorb bone by expelling lysosomal enzymes and carbonic acid onto the bone surface. The osteoclasts are closely adhered to the bone, and the area of bone resorption is called a 'Howships' lacuna'. A dense connective tissue called periosteum surrounds the outer surface of the bone. XB-IMG-158230
Figure 29.
Cardiac muscle. A. Longitudinal section of cardiac muscle. Cells are branched and have striations in the cytoplasm. B. Cross section of cardiac muscle. The nuclei are located centrally within the cell. XB-IMG-158234
Chapter 2: Cardiovascular System
Figure 2.
Lymphatic Vessels. Lymphatic vessels begin as blind-ended sacs Iacteals) that collect lymphatic fluid from the interstitial space of tissues, such as in the lamina propria of the duodenum shown here. These vessels are lines by an endothelium, and are often difficult to discern from veins. XB-IMG-158239
Figure 3.
Blood and lymphatic vessels. A. The lumen of a small artery is lines with endothelium with a layer of smooth muscle surrounding it. B. Arteries are often accompanied by peripheral nerves. C. Capillaries are composed of a single layer of endothelium, and the lumen is just large enough for an erythrocytes to pass. D-E. Arterioles are small arteries with smooth muscle around them.In longitudinal section, the smooth muscle cells are seen wrapping around the vessel, and are oriented perpendicular to the endothelium nuclei. F. Longitudinal section of a small artery. G. Longitudinal section of a capillary in skeletal muscle. H. A neurovascular bundle consists of a peripheral nerve, an artery, a vein, and a lymphatic vessel. XB-IMG-158240
Figure 4.
Low magnification of the heart. The outer surface of the heart is surrounded by an epicardium, and the inner surface by the endocardium. The two atria and the one ventricle are the chambers through which blood is pumped. XB-IMG-158241
Figure 5.
The atrium and ventricle. A. Atria are surrounded by the epicardium that consists of a layer of endothelium and some loose connective tissue containing blood vessels and nerves. The cardiac muscle is organized into thin strands. B. The myometrium of the ventricle is quite large, and is also surrounded by an epicardium. XB-IMG-158242
Figure 6.
Heart valves. A. low magnification of the valves of the heart. Blood flows between the atrium and ventricle through valves, composed of dense irregular connective tissue. B. High magnification of the heart valve. XB-IMG-158243
Figure 7.
Endocardium and myocardium. The luminal surface of the myocardium is lined by an endothelium, called the endocardium, which is a simple squamous endothelium. XB-IMG-158244
Chapter 4: Gastrointestinal System
Figure 1.
Low magnification image of the stomach. The lumen of the stomach is lined by a mucosa, which is comprised of an epithelium, lamina propria, and the muscularis mucosa. A muscularis externa is one of the most outer layers of the stomach. XB-IMG-158245
Figure 3.
Mucous membrane of the stomach. The surface layer of the mucosa is composed of simple columnar epithelium. Invaginations of the surface epithelium form gastric pits, which also lines with surface epithelium. Branching off of the gastric pits are gastric glands that aid digestion. The underlying loose connective tissue of the lamina propria contains many capillaries that transport absorbed nutrients into the circulation. The deepest layer of the mucosa is the muscularis mucosa, which is a layer of smooth muscle cells. XB-IMG-158246
Figure 7.
The duodenum of the small intestine. The first region of the small intestine is the duodenum. It has a large muscularis externa. The mucosa evaginates into the lumen as large villi, which serve to increase the absorptive surface area. XB-IMG-158247
Figure 12.
Low magnification image of the colon. A mucosa comprised of a surface epithelium and lamina propria line the lumen, and a thin musclaris externa forms the outer most layer. XB-IMG-158248
Figure 15.
The epithelium of the colon. The simple columnar epithelium of the colon contains mucous secreting goblet cells. Goblet cells reach the apical surface of the epithelium and release their contents via merocrine secretion (exocytosis). XB-IMG-158249
Figure 16.
Low magnification image of the liver. The liver is encapsulated by a dense connective tissue capsule. Within the parenchyma of the organ are many sinusoids. XB-IMG-158250
Figure 17.
The organization of the liver. The major cell type of the liver is the hepatocytes, which are joined together as cords, and are separated by numerous sinusoids. XB-IMG-158251
Figure 18.
High magnification image of liver cells. The hepatocytes are arranged into cords separated by venous sinusoids. Within the sinusoids are erythrocytes and leukocytes. Also within sinusoids are Kupffer cells, which are phagocytic and participate in the removal of senile erythrocytes. The cytoplasm of the hepatocytes has many vacuoles, which are made more visible by the extraction of glycogen during paraffin processing. Canaliculi are small channels between hepatocytes, which transport bile made by the hepatocytes to the bile ducts of the portal triads. XB-IMG-158252
Figure 21.
Route of bile flow in the liver. Bile that is produced in the hepatocytesis secreted into canaliculi, which are small channels between hepatocytes. Bile from the canaliculi drains into small ducts called canals of Hering, which transport the bile to the bile duct in the portal triad. XB-IMG-158253
Figure 22.
Canals of Hering. Bile is secreted from hepatocytes into the canaliculi, which merge to form the canals of Hering. The canals of Heirng transport bile to the bile duct in the portal triad. Bile is then transported via the entry hepatic duct to the gall bladder. XB-IMG-158254
Figure 23.
Low magnification image of the gall bladder. The lumen is lined by a simple columnar epithelium with an underlying lamina propria. XB-IMG-158255
Figure 26.
Muscularis of the gall bladder. Deep to the lamina propria of the gall bladder is a thin layer of smooth muscle that compromises the muscular. External to the muscular is the adventitia. XB-IMG-158256
Figure 27.
Low magnification image of the pancreas. The majority of the pancreas is comprised of exocrine pancreatic acinar cells that expel their contents through a series of ducts. XB-IMG-158257
Figure 32.
Ducts of the pancreas. A. Intralobular ducts are lined with simple cuboidal epithelium and have relatively large lumen. They transport secretions from the intercalated ducts to the interlobular ducts. B. Centroacinar cells line the lumen of the pancreatic acini and are continuous with intercalated ducts. Intercalated ducts are lined with a low cuboidal epithelium and have a very small lumen. They transport secretions from the pancreatic acinar cells to the intralobular ducts and also secrete bicarbonate and water. C. Interlobular ducts are located in connective tissue septa between lobules and receive secretions from the intralobular ducts. They are lined with a simple or stratified cuboidal epithelium. XB-IMG-158258
Chapter 5: Respiratory System
Figure 1.
Low magnification of sagittal section of Xenopus head. The respiratory tract begins at the external nares. XB-IMG-158259
Figure 2.
Chambers of the external nares. The external nares constricts to specifically admit air in the one chamber (1) that leads to the nasal cavity when the nares are above the water level. Below the water level, the nares constricts to admit water into a second chamber (2) lined with olfactory epithelium, thus enabling the frog to detect water-borne odorants. XB-IMG-158260
Figure 4.
Low magnification of a sagittal section of a frog head showing the location of the vomeronasal organ. The vomeronasal organ is located just above the oral cavity. XB-IMG-158290
Figure 5.
High magnification of the vomeronasal organ. The sensory epithelium is continuous with the respiratory epithelium of the nasal cavity. XB-IMG-158291
Figure 11.
Low magnification image of a lung. The trachea gives rise to paired bronchi, which enter the lungs and give rise to many bronchioles. These in turn give rise to the alveolar sacs, where gas exchange with the blood occurs. XB-IMG-158292
Figure 12.
Bronchus of a lung. Bronchi are supported with plates or rings of cartilage. The bronchi give rise to bronchioles, which are not associated with cartilaginous plates. Bronchioles have a layer of smooth underlying the epithelial mucosa. XB-IMG-158293
Figure 13.
Low magnification image of lung tissues. A visceral pleura forms the outer surface of the lung. Note the invaginations of the lung surface. Bronchi are identified by the presence of the basophilic hyaline cartilage. Bronchioles are identified by the presence of smooth muscle and lack of alveoli. XB-IMG-158304
Figure 14.
Bronchus of the lung. Bronchi are identified by the presence of hyaline cartilage and smooth muscle below the epithelial layer. Note the orientation of the smooth muscle cells (similar to the orientation of smooth muscle cells that occurs in arteries) in this oblique section. XB-IMG-158315
Figure 15.
High magnification of the visceral pleura. The outer surface is lined with a layer of simple squamous epithelium. The inner surface is often lined with alveolar capillaries where gas exchange occurs. XB-IMG-158316
Figure 16.
Alveolar sacs of the lung. he bronchioles, which are not lined with alveolar capillaries, give rise to alveolar sacs. Alveolar sacs are blind ended pouches lined with alveolar capillaries and pneumocytes. This is the location where gas exchange occurs with the erythrocytes. XB-IMG-158317
Chapter 6: Urinary System
Figure 2.
Organization of the kidney. The convoluted tubules are located in the cortex, and the more eosinophilic medulla contains collecting tubules that drain into progressively larger tubules to exit the kidney. XB-IMG-158319
Figure 6.
Major tubular structures of the cortex. Underlying the renal capsule are the major tubular structures of the cortex. The proximal convoluted tubules are eosinophilic cuboidal epithelium and are often found near the renal corpuscles. They have microvilli on their apical surface. Also near the renal corpuscles are the distal convoluted tubules which are cuboidal epithelium and have a basophilic appearance. These cells are often larger than the proximal tubules and has a similar eosinophilic staining quality. The cuboidal cells are larger and also have microvilli on their apical surface. Collecting tubules are quite basophilic, and are composed of two cell types; cuboidal epithelium and mucus-containing flask cells. XB-IMG-158320
Figure 7.
Renal corpuscles and other cortical structures. Most renal corpuscles are located very near the renal capsule. At the center of the renal corpuscle is the capillary-filled glomerulus. XB-IMG-158321
Figure 10.
High magnification of renal cortex. In addition to proximal and vital convoluted tubules and renal corpuscles, collecting tubules are also located in the renal cortex (and in the medulla). The cells compromising the collecting tubules are cuboidal epithelial cells and mucus-secreting cells called flask cells. XB-IMG-158388
Figure 15.
Renal corpuscles in the renal cortex. A. Ultrafiltrate in urinary space enters the proximal convoluted tubule at the urinary pole of the renal corpuscle. B. At the urinary pole of the renal corpuscle, the proximal convoluted tubule receives the ultrafiltrate. Note the presence of microvilli on the proximal tubule cells. C. Opposite from the urinary pole of the renal corpuscle is the vascular pole. The afferent and efferent arterioles enter and leave the glomerulus at the vascular pole. XB-IMG-158389
Figure 20.
Low magnification image of the urinary bladder. The lumen of the bladder is lined with transitional epithelium. Underlying the epithelium is a loose connective tissue called the lamina propria. The next layer is a layer of smooth muscle cells called the muscular. The outer layer is either an adventitia or serosa. XB-IMG-158390
Figure 21.
Epithelium and lamina propria of the urinary bladder. The layer of transitional epithelium overlies the lamina propria, which is composed of loose connective tissue. Note the presence of many blood vessels just below the epithelium basement membrane. XB-IMG-158391
Figure 22.
High magnification image of urinary bladder epithelium. The epithelium lining the lumen of the urinary bladder is transitional epithelium. Note the presence of two distinct cell types of the epithelium. The epithelial cells comprise most of the mucous lining and are stratified. Some epithelial cells appear cuboidal in shape, while other appear to be squamous. Interspersed among the epithelial cells are mucus-containing cells that have the same appearance as the flask cells of the collecting tubules of the kidney. XB-IMG-158415
Chapter 7: Endocrine Organs
Figure 1.
Low magnification of a sagittal section of a frog head, containing the pituitary gland. The pituitary gland (hypophysis) is attached to the floor of the diencephalon of the brain by an infundibular stalk. It receives hormonal signals from nuclei of the hypothalamus, which control the secretion of hormones from the pituitary gland. XB-IMG-158416
Figure 2.
Pituitary gland. The pituitary gland is comprised of the adenophyophysis, which contains the pars distills and pars intermedia, and the neurohypophysis, which contains the pars nervosa and median eminence, The pituitary gland is attached to the hypothalamus by the infundibular stalk. XB-IMG-158417
Figure 9.
Low magnification image of the roof of the diencephalon containing the pineal gland. The pineal glad (epiphysis) is attached to the brain in the region of the left and right habenular nuclei. XB-IMG-158418
Figure 10.
High magnification of the pineal gland. Ependymal cells line the third ventricle. The principal cells of the pineal gland are pinealocytes (also called epiphyseal epithelium), which produce the hormone melatonin. In Xenopus, the pinealocytes have an appearance similar to retinal photoreceptors with outer segments that protrude into the lumens of the gland. Interstitial cells are glial-like cells and are identified by their elongate or irregular-shaped nuclei. XB-IMG-158419
Figure 11.
Low magnification of sagittal section of Xenopus head. The thyroid gland is a bi-lobed organ located in the neck region just ventral to the larynx. XB-IMG-158420
Figure 12.
Intermediate magnification image of the thyroid gland. The thyroid gland is composed of spherical colloid-filled follicles that are lined by follicular cells. The follicular cells produce thyroid hormones by the production of thyroglobulin, which is stored in the extracellular colloid. At the basal side of the follicular cells is an extensive capillary plexus. XB-IMG-158421
Figure 14.
Low magnification image of the adrenal gland. The adrenal glad of Xenopus leaves is also called the internal gland because of its position in the medial regions of the kidneys are apposed to each other. The adrenal gland appears as clusters of chromaffin cells and adrenaocortical cells just within the renal capsule. XB-IMG-158422
Chapter 8: Reproductive Organs
Figure 1.
Low magnification image of the ovary. The ovary is comprised primarily of many oocytes clustered together. XB-IMG-158424
Figure 2.
Oocytes comprise most of the ovary. Mature oocytes have a dimatere about 1.5mm. A large nucleus can be observed in most oocytes, and a layer of pigment granules closely underlie the plasma membrane. XB-IMG-158425
Figure 3.
Oocyte nucleus. The nuclei of oocytes have many nucleoli that tend to be located near the nuclear envelope. A Balbiani body, which is a large mass of mitochondria, is located close to the nucleus. Within the cytoplasm are many small membrane-bound structure called yolk platelets, which provide nutrition for the developing embryo. XB-IMG-158426
Figure 4.
Oocyte cytoplasm and membrane. Cortical granules are located near the plasma membrane, and a layer of pigment granules closely underlie the membrane. Flattened follicular cells are on the extracellular side of the oocyte membrane. A delicate theca layer overlies the follicular cells. XB-IMG-158427
Figure 5.
Low magnification image of a cross section of the oviduct. The lumen of the oviduct is lined by many glands that secrete into the lumen. A fibrous stroma supports the basal portion of the glands. XB-IMG-158428
Figure 6.
Longitudinal section of the oviduct. The oviduct is surrounded by a layer of dense connective tissue. Long glands empty their secretory products into the lumen as oocytes travel along the lumen from the ovary. The glandular secretions form the layers of jelly coats on the oocytes as they are transported to the cloaca. XB-IMG-158430
Figure 7A.
High magnification images of oviduct glands. A) Longitudinal orientation of the oviduct glands. The glandular cell nuclei are located at the basal side of the cells and secrete their contents into the glandular lumen that is confluent with the lumen of the oviduct. The epithelial cells lining the oviduct lumen are ciliated, and aid in the transport of oocytes from the ovaries to the cloaca. XB-IMG-158473
Figure 7B.
High magnification images of oviduct glands. B) Horizontal orientation of the oviduct glands. The glandular lumen is is located centrally, and the glands are surrounded by loose connective tissue with many capillaries. Note the dark-staining secretory granules that contain mucin-like glycoproteins that are secreted to make the layers of jelly coats on the oocytes as they are transported through the lumen. XB-IMG-158484
Figure 8.
Low magnification image of the testes. The testes are surrounded by a dense connective tissue capsule. The mediastinum receives spermatids that are produced in seminiferous tubules, which comprise most of the testes. XB-IMG-158487
Figure 9.
Seminiferous tubules of the testes. The seminiferous tubules are surrounded by loose connective tissue and this area is called the intertubular space. In this speciment the space between each seminiferous tubule and the connective tissue of the intertubular space is an artifact of the paraffin embedding process. The seminiferous tubules are confluent with the straight tubules (also called tubuli recti) through which the spermatids travel to the rete testes of the mediastinum and from there will exit the testes. XB-IMG-158488
Chapter 9: Integument
Figure 1.
Low magnification image of Xenopus skin. The skin (integument) is composed of the epidermis and dermis. Within the dermis are many glands that secrete material to the surface. XB-IMG-158489
Figure 2.
The integument of Xenopus leaves. Lateral line organs protrude from the epithelium to the surface. Mucous glands and serous glands secretes materials through excretory ducts to the surface. The dermis is composed of dense connective tissue. XB-IMG-158490
Figure 3.
The epidermis. The epithelium of the epidermis is a keratinized stratified squamous epithelium, and is composed of four distinct layers; the stratum corner, stratum granulosum, stratum spinosum, and stratum basale. A thin stratum lucid also appears between the corneum and granulosum. Melanocytes are present throughout the epithelium. XB-IMG-158508
Figure 4.
The dermis. Mucous and serous glands are prominent in the dermis, and expel their secretory contents to the surface of the epidermis through excretory ducts. The dense connective tissue (CT) of the dermis is dense irregular CT, which is close to the epidermis, and the CT of the more distal region of the dermis is composed of dense regular CT. XB-IMG-158509
Figure 5.
The dermis. Directly underlying the epidermis is the loose connective tissue (CT) of the dermis, which contains many capillaries. Deep to the loose CT is the dense irregular CT of the dermis, and deep to that is the dense regular CT of the dermis. XB-IMG-158553
Figure 6.
Exocrine glands of the skin. A) Mucous glands are prominent in the integument and secreted mucus through an excretory duct composed of cuboidal epithelium. The mucous cell have a highly vacuolated cytoplasm and a round nucleus. B) The protein secreting glands of the skin (also called granular cells) secrete their proteinaceous products through an excretory duct composed of cuboidal epithelium. Unlike the mucous gland cells, these granular cells constitute a syncytium (fusion of several cells). XB-IMG-158555
Figure 7.
Lateral line organs of the skin. The lateral line organs are small, elongated structures on the head and trunk of Xenopus. Hair cells on the surface are called neuromasts an respond to a flow of water over the surface. Each neuromast consists of a group of cells embedded in the epidermis. The mantle cells lie peripherally and surround the centrally positioned sensory and supporting sustentacular cells. The sustentacular cells extend from the basement membrane to the outer surface. The sensory hair cells extend to the free surface, but to not reach the basement membrane. The sensory hairs of the hair cells consist of one kinocilium and 20-40 stereo cilia which are enclosed by a gelatinous cupola. The basal cells are attached to the basement membrane but do not reach the free surface. XB-IMG-158556
Figure 8.
Innervation of lateral line organs. The lateral line organs are embedded in the epidermis, and are innervated by sensory nerve fibers that pass through the dermis. The lateral line sensory system functions to detect and localize movements of nearby obstacles, prey, predators, and con-specifics in the environment. XB-IMG-158557
Chapter 10: Cranial Structures
Figure 1.
Low magnification image of the Xenopus cranium in the parasagittal plane. The rostral side of the head is to the right. XB-IMG-158562
Figure 14.
The epiglottis. The epiglottis is a movable tissue that covers the larynx during swallowing preventing food from gaining access to the trachea. It is open (displaced in a rostral direction) during respiration. XB-IMG-158575
Figure 18.
Low magnification images of the esophagus. The esophagus is dorsal to the trachea that is encased in cartilage. XB-IMG-158576
Figure 21.
Microscopic image of three nasal chambers. Inset shows the plane of section in the parasagittal plane. The middle chamber is rostral (to the right), the principal cavity is caudal, and the vomeronasal organ is ventral to both other chambers. The principal cavity opens into the roof of the mouth as the internal naris. XB-IMG-158583
Figure 26.
Vomeronasal epithelium. The vomeronasal mucosa is unique in that it surrounds a very narrow lumen, the sensory cells possess only microvilli, which are seen as very long membranous extensions of the sensory cell dendrite into the lumen, and the sustentacular cells occupy a very distinct layer separated from the sensory cells. XB-IMG-158584
Figure 27.
High magnification image of respiratory mucosa from a ventrocaudal area of the nasal cavity just caudal to the vomeronasal organ. The respiratory epithelium contains numerous ciliated cells and mucous cells. Basal cells located at the base of the epithelium give rise to new respiratory cells. Underlying the epithelium is a typical lamina propria. XB-IMG-158589
Figure 29.
Low magnification image of a parasagittal section of Xenopus brain showing three of the brain divisions. Inset shows plane of section. XB-IMG-158590
Figure 39.
High magnification image of the optic chiasm and optic tract. The optic chiasm is the region in which axons from ganglion cells of the retina cross to project to the opposite side of the brain. These axons continue caudally in the optic tract. XB-IMG-158591
Figure 47.
Low magnification image through two canals of the inner ear cistern. The horizontal canal is oriented in cross-section and the rostral vertical canal is oriented obliquely. Cristae appear as crescents of sensory and supporting cells. XB-IMG-158592
Figure 48.
High magnification image of the cristae from the horizontal canal. XB-IMG-158608
Figure 61.
Low magnification image of the eye of a Xenopus in parasagittal plane, showing the outer surface the eye, the cornea, the position of the lens, iris and retina. he sclera contains a cartilaginous layer that adds extra support to the eye. XB-IMG-158227
Figure 66.
High magnification of the cornea. The cornea is a multilayered structure consisting of a non-pigmented stratified squamous epithelium, a connective tissue storm and an endothelium adjacent to the aqueous chamber of the eye. The squamous epithelium of the cornea is continuous with the integument of the head. The corneal stoma is continuous with the sclera. XB-IMG-158609
Figure 69.
High magnification image of the retina. The retina is a layered structure. The photoreceptors respond to photons of light that pass through the retina, and the neural signal is transmitted through the retinal layers to the ganglion cells. There are both rod and cone photoreceptors in the Xenopus retina, and the distal portions of the rod outer segments are intimately associated with the apical microvilli of the pigment epithelium. XB-IMG-158610
Figure 70.
High magnification image of the Xenopus laevis retina. The outer choroid layer is pigmented vascular layer. The choriocapillaris is a capillary layer in the chord and is in direct contact with the basal surface of the retinal pigmented epithelium (RPE). It supplies the photoreceptors with oxygen and nutrients. The fused basement membrane of the choriocapillaris and the RPE is termed Bruch's membrane (*). The RPE cells phagocytize distal photoreceptor outer segments that are shed under a cyclic rhythm. XB-IMG-158611
Last Updated: 2019-09-01