Ventral Protrusion Research Articles

Anatomical Variation of the Origin of the Right Renal Artery : Assessment with an Angle of the Origin and Ventral Protrusion

The right renal artery has been considered to originate laterally from the anterior aspect of aorta. In some cases, it turns more ventrally than the aorta, which can lead to intraoperative right renal artery injury. For this reason, we evaluated how the right renal artery turns ventrally and analyzed the factors for ventral protrusion of the right renal artery. We examined contrast-enhanced computed tomography images of 195 individuals and measured their angles of the right renal artery and ventral protrusion from the aorta. Age and sex had no significant correlation with these variations. A weaknegative correlation was found between body mass index and these variations. Almost all the right renal artery originated from the ventral side of the aorta, and almost half the right renal artery arose ventrally more than the aorta. Careful attention should be paid to ventral protrusion of the right renal artery to prevent vascular injury during surgery using the anterior approach to the upper retroperitoneum.

Ultrasonographic features associated with the lumbosacral or lumbar 5–6 symphyses in 64 horses with lumbosacral‐sacroiliac joint region pain (2012–2018)

SummaryThe ultrasonographic appearance of the lumbosacral symphysis of horses with no history of hindlimb lameness or thoracolumbosacral pain has previously been documented. The aims of the study were to describe the signalment and clinical findings in horses with ultrasonographic lesions of the fifth and sixth lumbar (L) vertebrae and lumbosacral symphyses and to determine whether lesions of the L5‐6 symphysis are only seen in horses with congenital sacralisation or other abnormalities of the lumbosacral symphysis. Horses in Group 1 (n = 25) underwent poor performance investigation and improved in ridden performance after infiltration of mepivacaine around the sacroiliac joints. Horses in Group 2 (n = 39) presented for investigation of changes in thoracolumbosacral shape or poor performance but did not undergo anaesthesia of the sacroiliac joint regions. The median ages were 10 and 19 years respectively for Groups 1 and 2. Mares (53.1%) were over‐represented relative to the normal populations of the clinics. All horses had poor development of the thoracolumbar epaxial and pelvic muscles and prominence of the lumbar spinous processes and the tubera sacrale. Most horses (70%) had reduced range of movement of the thoracolumbosacral region. Ultrasonographic features included irregular vertebral end plates; heterogeneous echogenicity of the intervertebral disc ± ventral protrusion; and displacement of the ventral longitudinal ligament ± alteration in its echogenicity. In Group 1, abnormalities of the L5‐6 symphysis were seen in 13 horses, of which 84.6% had congenital sacralisation or narrowing of the lumbosacral symphysis. In Group 2, the majority of horses had lesions of both the L5‐6 and lumbosacral symphyses; only 9/39 horses (23.1%) had congenital fusion of either joint. Limitations include the lack of age‐matched control horses. However, the purpose of the study was to raise awareness of lesions of the L5‐6 and lumbosacral symphyses, which may contribute to pain and poor performance.

The family Ascothoracidae Grygier, 1987, a review with descriptions of new abyssal taxa parasitizing ophiuroids and remarks on the invalidity of the genus Parascothorax Wagin, 1964 (Crustacea: Thecostraca: Ascothoracida)

Two new ascothoracidan species in the family Ascothoracidae Grygier, 1987, Ascothorax rybakovi sp. nov. and Cardiosaccus pedri gen. et sp. nov., are described from the Kuril-Kamchatka Trench at abyssal depths of 5150–5700 m. They are among the deepest known ascothoracidans. They live as mesoparasites in permanent cysts within the bursae of the brittle stars Ophiacantha pacifica Lutken and Mortensen, 1899 and Amphiophiura pacifica Litvinova, 1971, respectively. This is the first study of new forms of Ascothoracidae in which SEM has been used in the descriptions, including the lattice organs and the early nauplius. Cardiosaccus differs from Ascothorax in displaying the following apomorphic traits: (i) absence of thoracopod 1; (ii) a smaller fifth antennular segment that is completely fused with the claw; (iii) absence of small setae at the base of this claw; and (iv) an extremely large ventral protrusion of the fourth abdominal segment. Material of Parascothorax synagogoides Wagin, 1964 from near the type locality, studied with SEM, could not be distinguished from Ascothorax by any reliable morphological criteria. Cyst structure and the manner of cyst formation cannot be used, because although cyst is the result of the parasites activity, this is a feature of the host, not something inherent to the parasite. Moreover, the inferred settlement of the larvae of P. synagogoides on the outer edge of the bursal slit is best regarded as plesiomorphic behavior, reflecting how the Ascothoracidae became bursal mesoparasites in the first place. We therefore regard Parascothorax as invalid and refer P. synagogoides to Ascothorax. Within the family Ascothoracidae as now constituted, Ascothorax is cosmopolitan and speciose and includes species that exclusively infect a single host species, whereas Cardiosaccus is monotypic and restricted to the northwest Pacific. Ascothorax rybakovi sp. nov. is the third species of this genus known to harbor hyperparasitic cryptoniscid isopods.

A New Species ofMyrmecina(Hymenoptera: Formicidae) from Southeastern North America

A new species of ant, Myrmecina cooperi sp. nov. (Hymenoptera: Formicidae: Myrmecinae) is described and illustrated from specimens collected in Florida and Alabama, USA. This species is characterized by its small size (under 2 mm length), shagreened gastral tergites, and a strong ventral protrusion on the underside of the postpetiole. It is presently known from a small area in the Florida Panhandle and adjacent Alabama. Habitus illustrations and an identification key are provided for the 3 eastern species of Myrmecina.

Metamorphic remodeling of morphology and the body cavity in Phoronopsis harmeri (Lophotrochozoa, Phoronida): the evolution of the phoronid body plan and life cycle.

BackgroundPhoronids undergo a remarkable metamorphosis, in which some parts of the larval body are consumed by the juvenile and the body plan completely changes. According to the only previous hypothesis concerning the evolution of the phoronid body plan, a hypothetical ancestor of phoronids inhabited a U-shaped burrow in soft sediment, where it drew the anterior and posterior parts of the body together and eventually fused them. In the current study, we investigated the metamorphosis of Phoronopsis harmeri with light, electron, and laser confocal microscopy.ResultsDuring metamorphosis, the larval hood is engulfed by the juvenile; the epidermis of the postroral ciliated band is squeezed from the tentacular epidermis and then engulfed; the larval telotroch undergoes cell death and disappears; and the juvenile body forms from the metasomal sack of the larva. The dorsal side of the larva becomes very short, whereas the ventral side becomes very long. The terminal portion of the juvenile body is the ampulla, which can repeatedly increase and decrease in diameter. This flexibility of the ampulla enables the juvenile to dig into the sediment. The large blastocoel of the larval collar gives rise to the lophophoral blood vessels of the juvenile. The dorsal blood vessel of the larva becomes the definitive median blood vessel. The juvenile inherits the larval protocoel, mesocoel, and metacoel. Late in metamorphosis, however, the protocoel loses its epithelial structure: the desmosomes between cells and the basal lamina under the cells disappear. This loss may reflect a reduction of the protocoel, which is a characteristic of some recent phoronids.ConclusionsBased on our investigation of P. harmeri metamorphosis, we hypothesize that the phoronid ancestor was worm-like animal that possessed preoral, tentacular, and trunk coeloms. It lived on the soft sediment and collected food with its tentacles. When threatened, this worm-like ancestor buried itself in the soft sediment by means of the ventral protrusion into which the loop of the intestine and the blood vessels were drawn. We propose that this behavior gave rise to the body plan of all recent phoronids. The evolution of phoronid life cycle seems having more in common with“intercalation” than “terminal addition” theories.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0504-0) contains supplementary material, which is available to authorized users.

Functional morphology and kinematics of terrestrial feeding in the largescale foureyes (Anableps anableps).

A major challenge for aquatic vertebrates that invade land is feeding in the terrestrial realm. The capacity of the gape to become parallel with the ground has been shown to be a key factor to allow fishes to feed on prey lying on a terrestrial surface. To do so, two strategies have been identified that involve a nose-down tilting of the head: (1) by pivoting on the pectoral fins as observed in mudskippers, and (2) curling of the anterior part of the body supported by a long and flexible eel-like body as shown in eel-catfish. Although Anableps anableps successfully feeds on land, it does not possess an eel-like body or pectoral fins to support or lift the anterior part of the body. We identified the mechanism of terrestrial prey capture in A. anableps by studying kinematics and functional morphology of the cranial structures, using high-speed video and graphical 3D reconstructions from computed tomography scans. In contrast to the previously described mechanisms, A. anableps relies solely on upper and lower jaw movement for re-orientation of the gape towards the ground. The premaxilla is protruded anteroventrally, and the lower jaw is depressed to a right angle with the substrate. Both the lower and upper jaws are selectively positioned onto the prey. Anableps anableps thereby uses the jaw protrusion mechanism previously described for other cyprinodontiforms to allow a continued protrusion of the premaxilla even while closing the jaws. Several structural adaptations appear to allow more controlled movements and increased amplitude of anterior and ventral protrusion of the upper jaw compared with other cyprinodontiforms.

CLINICAL AND ANATOMICAL ASPECTS OF TESTICLE DESCENT INTO THE SCROTUM

By means of morphological methods of examination it was found that gubernaculum of the testis, which rudiments appear at the beginning of the 6th week of embryogenesis, plays a leading role in the testicle descent into the scrotum. Accelerated formation of gubernaculum of the testis in 5-8 monthold fetuses which is proved by the prevalence of smooth muscular cells over the elements of the connective tissue, is one of the main factors of heterochrony in the testicle development and their further descent into the scrotum. The ventral protrusion of the peritoneum vaginal process appears at the end of the 8th week of embryogenesis; formation of the process is prior to caudal displacement of the testes. The fusion of the visceral plate of the peritoneum vaginal process with protein membrane of the testis and over testis occurs in 6-7 month-old fetuses. Disorders in the process of fusion of the layers of processus vaginalis peritonei in 9-10-month-old fetuses may be anatomic precondition of congenital inguinoscrotal hernia development.

The duckweed Wolffia microscopica: A unique aquatic monocot

The rediscovered species Wolffia microscopica (Griff.) Kurz, endemic to India, Pakistan and Bangladesh, shows several features that make it unique in comparison to other duckweeds, even to other species of the genus Wolffia. During vegetative propagation, the daughter fronds are produced by budding within a single pouch of the mother frond. Several generations of fronds and their initials exist in union with the parent frond at a given time. Most strikingly, almost all the fronds flower, both in nature and under controlled culture conditions. Thus, in contrast to all other duckweed species, generative propagation is as important as vegetative propagation, which opens the opportunity for artificial breeding. Moreover, flower development on both mother and daughter fronds was observed at the same time. In contrast to all other duckweed species, fronds of W. microscopica often possess a ventral projection of varying length ranging from an almost flat appearance of the ventral surface to a length of 4mm. Absence of root cap, root hairs and vascular tissue demonstrate that this ventral protrusion is not a root and accordingly we name this special structure “pseudoroot”. The high number of chloroplasts in the pseudoroot may result in higher capacity of photosynthesis without increasing the frond area which covers the water surface. Thus we propose that the pseudoroot serves to be advantageous to W. microscopica in multiplying at a faster rate in comparison to other duckweeds.

Relationship between ventral lumbar disc protrusion and contrast medium leakage during sympathetic nerve block

Ventral disc protrusions have been neglected because they are asymptomatic. Lumbar sympathetic nerve block (LSNB) is one of the clinical choices for refractory low back pain treatment. Leakage of the contrast medium may occur and lead to complications, especially when using a neurolytic agent. In this study, we retrospectively reviewed the magnetic resonance images (MRIs) of 52 consecutive patients with refractory low back pain due to lumbar spinal canal stenosis who underwent LSNB, and graded ventral disc protrusion at the L1/2 to L5/S1 vertebral discs on a three-point scale (grade 0 = no protrusion, grade 1 = protrusion without migration, grade 2 = protrusion with migration). We also determined if there was leakage of contrast medium in LSNB. Ventral disc protrusion was observed in all patients, and 75 % (39/52) had grade 2 protrusion in the L1/2-L3/4 vertebral discs. Moreover, the incidence of contrast medium leakage was significantly higher at the vertebrae that had grade 2 protrusion than at those with less protrusion. We revealed a higher incidence of ventral disc protrusion of the lumbar vertebrae than previously reported, and that the incidence of leakage in LSNB increased when ventral disc protrusion was present. To avoid complications, attention should be paid to ventral disc protrusions before performing LSNB.

Shoulder injuries: is there a characteristic syndrome of 'snowboarder's shoulder'?

Injured shoulders have been examined by a new technique, which, it is believed, shows a previously unrecognised, typical muscle imbalance. The long head of the triceps, the pectoralis major and the biceps brachii are involved and changes in their muscle tone have been detected. It is believed that this causes ventral (anterior) protrusion of the humeral head and consequent instability of the glenohumeral joint. The paper describes the method of examination and treatment of these cases. Further work is required to show the validity of these findings and whether this pattern is seen most frequently in snowboarders.

Fgf10 maintains notch activation, stimulates proliferation, and blocks differentiation of pancreatic epithelial cells.

The pancreas is an endodermally derived organ that initially appears as a dorsal and ventral protrusion of the primitive gut epithelium. The pancreatic progenitor cells present in these early pancreatic anlagen proliferate and eventually give rise to all pancreatic cell types. The fibroblast growth factor receptor (FGFR) 2b high-affinity ligand FGF10 has been linked to pancreatic epithelial cell proliferation, and we have shown previously that Notch signalling controls pancreatic cell differentiation by means of lateral inhibition. In the developing pancreas, activated intracellular Notch appears to be required for maintaining cells in the progenitor state, in part by blocking the expression of the pro-endocrine gene neurogenin 3 (ngn3), and hence endocrine cell differentiation. Here, we show that persistent expression of Fgf10 in the embryonic pancreas of transgenic mice also inhibits pancreatic cell differentiation, while stimulating pancreatic epithelial cell proliferation. We provide evidence that one of the effects of the persistent expression of Fgf10 in the developing pancreas is maintained Notch activation, which results in impaired expression of ngn3 within the pancreatic epithelium. Together, our data suggest a role for FGF10/FGFR2b signalling in regulation of pancreatic cell proliferation and differentiation and that FGF10/FGFR2b signalling affects the Notch-mediated lateral inhibition pathway.

Functional morphology of prey capture in the sturgeon, Scaphirhynchus albus

Acipenseriformes (sturgeon and paddlefish) are basal actinopterygians with a highly derived cranial morphology that is characterized by an anatomical independence of the jaws from the neurocranium. We examined the morphological and kinematic basis of prey capture in the Acipenseriform fish Scaphirhynchus albus, the pallid sturgeon. Feeding pallid sturgeon were filmed in lateral and ventral views and movement of cranial elements was measured from video sequences. Sturgeon feed by creating an anterior to posterior wave of cranial expansion resulting in prey movement through the mouth. The kinematics of S. albus resemble those of other aquatic vertebrates: maximum hyoid depression follows maximum gape by an average of 15 ms and maximum opercular abduction follows maximum hyoid depression by an average of 57 ms. Neurocranial rotation was not a part of prey capture kinematics in S. albus, but was observed in another sturgeon species, Acipenser medirostris. Acipenseriformes have a novel jaw protrusion mechanism, which converts rostral rotation of the hyomandibula into ventral protrusion of the jaw joint. The relationship between jaw protrusion and jaw opening in sturgeon typically resembles that of elasmobranchs, with peak upper jaw protrusion occurring after peak gape.

ULTRASTRUCTURE OF GYMNODINIUM AUREOLUM (DINOPHYCEAE): TOWARD A FURTHER REDEFINITION OF GYMNODINIUM SENSU STRICTO

Examination of the ultrastucture of the unarmored dinoflagellate Gymnodinium aureolum (Hulburt) G. Hansen (syn: Gyrodinium aureolum Hulburt) revealed the presence of nuclear chambers, which are specialized differentiations of the nuclear envelope, similar to those described in the type species of Gymnodinium, G. fuscum (Ehrenberg) Stein and certain other Gymnodinium species. The nuclear pores were restricted to these chambers. In the flagellar apparatus a nuclear fibrous connective linked the longitudinal microtubular root and the nucleus. This structure had so far been observed only in Gymnodinium spp. and in the heterotrophic species Actiniscus pentasterias (Ehrenberg) Ehrenberg, Nematodinium armatum (Dogiel) Kofoid et Swezy and Polykrikos kofoidii Chatton. Another unusual feature of G. aureolum was the presence of a striated fiber in the longitudinal flagellum, a feature previously only found in Ceratium furca (Ehrenberg) Claparède et Lachmann and C. tripos (O.F. Müller) Nitzsch. Gymnodinium aureolum also possessed a prominent ventral protrusion associated with the peduncle and containing electron opaque material. It is concluded that G. aureolum belongs to the Gymnodinium sensu stricto group. This may be a temporary classification, however, because G. aureolum and its allies differ from the type species G. fuscum by the presence of a transverse striated root, striated collars, trichocysts, and a peduncle.

Clarification of the process of separation of the cloaca into rectum and urogenital sinus in the rat embryo

Background/Purpose: The normal process of division of the cloaca into a rectum and urogenital tract is still not fully understood. The main controversies relate to how the urorectal septum (URS) divides the cloaca and whether the URS fuses with the cloacal membrane. This study used a 3-dimensional reconstruction technique, combined with histologic correlation, to observe the developmental and septational processes of the cloaca of the normal rat embryo from gestational days 11 to 16. Methods: Normal rat embryos from gestational days 11 to 16 were sectioned serially both transversely and sagittally and stained with H&E. 3-dimensional reconstructions were performed on embryos younger than day 13.5. The relevant structures were examined in a temporo-spatial sequence. Results: The tailgut started to regress by apoptosis on day 12 in a cranio-caudal direction. The URS, first evident in day-12.5 embryos, extended and fused with the cloacal membrane on day 15 of gestation, completing the separation of the cloaca into rectum and bladder. Regression of the tailgut and ventral protrusion of the urogenital sinus markedly changed the configuration of the cloaca. The cloacal membrane did not break down until after it had fused with the URS. Conclusions: These findings clarify the relative contributions made by active septation of the cloaca by the URS and configurational changes of the cloaca to produce a rectum and bladder. The URS fuses with the cloacal membrane before the anal and urogenital membranes break down. J Pediatr Surg 35:1810-1816. Copyright © 2000 by W.B. Saunders Company.

Analysis of the effects of the cdaK1 mutation of Tetrahymena thermophila on the morphogenesis of the fission line

Summary During divisional morphogenesis of a polarized ciliate cell, a single pattern of distribution of cortical structures along the main body axis is gradually transformed into a metameric chain made up of two sets of cortical structures belonging to the prospective anterior and posterior daughter cells. In an advanced stage of division in wild type Tetrahymena thermophila and in the cdaK1 mutant strain grown at the permissive temperature, a fission line boundary appeared in the form of equatorial gaps in the ciliary rows. An epitope of one of the major components of the membrane skeleton (epiplasm) transiently diminished posterior to this fission line and in the vicinities of the anterior and new posterior oral apparatuses. The changes in the distribution of this epitope depended upon the cell cycle. At a restrictive temperature (37°C), cdaK1 mutant cells displayed abnormal phenotypes in a late stage of cell division in cells delayed in cytokinesis. A localized decrease of immunostaining of epiplasm first appeared on the ventral surface of dividing cell along with fission line gaps at the normal central position, with a lengthening of the ventral cortex between oral apparatuses, but was delayed at some other neighbouring longitudes. Fission line gaps appeared at remaining lateral and dorsal longitudes but on anterior latitudes. During cytokinesis, the ventral cortex bulged and formed a ventral protrusion of the prospective anterior daughter cell. This resulted in an anterior translation of the final position of the fission line. An inhibitor of the serine/threonine kinase activity, 6-DMAP, applied to cdaK1 cells at a permissive temperature, yielded some dividing cells exhibiting cdaK1 phenotypes, with similar patterns of decrease of epiplasmic epitope, localized budding off a part of the cortex, and anterior displacement of the fission line. This suggests, a 6-DMAP and temperature-sensitive cell cycle-dependent coupling of patterned growth and subdivision of cell cortex with spatial distribution of the epiplasmic epitope of Tetrahymena. In cdaK1 cells, the post-telophase migration of micronuclei adjusted to the modified anterior position of the defective fission line. This process was arrested by nocodazole but was only indirectly affected by cytochalasin B.

Nematodes from the Strait of Magellan and the Beagle Channel (Chile): description of four new species of the Comesomatidae.

Four nematode species of the Comesomatidae from the Strait of Magellan and the Beagle Channel, Chile, are described as new to science. Comesoma hermani n. sp. can be separated from similar species, Comesoma bermudense Jensen & Gerlach, 1977, Comesoma minimum Chitwood, 1937 and Comesoma chilense Jensen & Gerlach, 1977 by the difference of body length, cephalic setae length, the ratio of the subcephalic setae to cephalic setae length and the ratio of spicule to anal body diameter. Dorylaimopsis magellanense n. sp. is identified by the lateral differentiation of 3–4 longitudinal rows of enlarged dots, the curved spicules are prominently jointed and with a ventral protrusion. Hopperia beaglense n. sp. could be easily recognised by both the rounded tail tip and anterior head end which differs from all the species of this genus except H. dorylaimopsoides (Allgen, 1959), which has, however, a smaller de Man ratio 'a' and reflexed ovaries. Hopperia arntzi n. sp. has a shorter body length which differs from the closest species, Hopperia americana Ward, 1984 and Hopperia muscatensis Warwick, 1973. Furthermore, the de Man ratio 'a' is different between our specimens and the other two species. An identification key to all known species of the genus Hopperia is provided.

Ovipositor mechanics of the braconine wasp genusZaglyptogastraand the ichneumonid genusPristomerus

The multiply-arched, apical quarter to half of the ovipositors of Zaglyptogastra species are capable of flexing ventrally through up to 180°. Flexion is achieved by ventral protrusion of the lower ovipositor valves relative to the upper one, an action which juxtaposes swollen lower valve sections with weak concave narrowings of the upper valve. The structural modifications associated with this flexion mechanism are described and similar ovipositor features are illustrated for the cremastine ichneumonid genus Pristomerus.

Cell-substratum interaction of cultured avian osteoclasts is mediated by specific adhesion structures.

The cell-substratum interaction was studied in cultures of osteoclasts isolated from the medullary bone of laying hens kept on low calcium diet. In fully spread osteoclasts, cell-substratum adhesion mostly occurred within a continuous paramarginal area that corresponded also to the location of a thick network of intermediate filaments of the vimentin type. In this area, regular rows of short protrusions contacting the substratum and often forming a cup-shaped adhesion area were observed in the electron microscope. These short protrusions showed a core of F-actin-containing material presumably organized as a network of microfilaments and surrounded by a rosette-like structure in which vinculin and alpha-actinin were found by immunofluorescence microscopy. Rosettes were superposable to dark circles in interference-reflection microscopy and thus represented circular forms of close cell-substratum contact. The core of ventral protrusions also contained, beside F-actin, fimbrin and alpha-actinin. Villin was absent. This form of cell-substratum contact occurring at the tip of a short ventral protrusion differed from other forms of cell-substratum contact and represented an osteoclast-specific adhesion device that might also be present in in vivo osteoclasts as well as in other normal and transformed cell types.

Disc Protrusion in the Cat: Ventral Protrusions and Radial Splits

SUMMARY Ventral protrusions and radial splits of the intervertebral discs have been investigated in 100 adult cats, 50 being of known age. Forty-eight of the latter were also examined for osteophytes. The ventral protrusions were either diffuse mounds or discrete knobs; clear splits of the annulus usually led towards the protrusion, but the annulus was seldom completely perforated. They were found in 23 cats. Forty-nine discs were affected, most of them (69 per cent) being between T10 and S1. There were no true lateral protrusions. In 15 cats with ventral protrusions there were 189 discs with osteophytes, and 21 of these had a ventral protrusion as well: 12 other discs had ventral protrusions, but no osteophytes. It cannot be said that osteophytes cause ventral protrusions, nor vice versa, but there was some statistical evidence that they may share causal factors in the cervical and lumbar regions. Radial splits consisted of outward distortion or radial rupture of lamellae unaccompanied by protrusion. These were found in 27 cats, affecting 43 discs, most of which (58 per cent) lay between T10 and S1, Ventral splits accounted for 60 per cent, and these occurred mostly between T10 and S1. Dorsal splits (19 per cent) were mainly cervical. Lateral splits (21 per cent) were irregularly scattered. Radial splits may be precursors of protrusions. Radial splits first occurred at 6 years old, ventral protrusions at 10. Over 80 per cent of both were found in cats 14 years old or more; therefore, both are essentially phenomena of senility. The nucleus pulposus was still gelatinous in 20 per cent of discs with ventral protrusions and 9 per cent with radial splits. This casts doubt on the orthodox concept that protrusions originate from degeneration of the nucleus pulposus. The findings suggest that one set of anatomical or biomechanical factors is needed to explain the distribution of dorsal protrusions and another for ventral protrusions. The low incidence of radial splits and ventral protrusions in the first 9 thoracic discs indicates that the conjugal ligament is not the only factor restricting dorsal protrusion in this region.