Postnatal Development of the Lower Canine and Cheek Teeth of the Pig

Postnatal development of the teeth of German Landrace and Göttingen Miniature pigs was studied by measuring the areas of each tooth visible on lateral radiographs of the mandibles. It was concluded that the appearance of the teeth at each stage, and the relation of their growth to that of the rest of the masticatory apparatus, relates mainly to postnatal changes in the relative location of the jaw pivot.     

Prenatal Dental Development in the Dog, Canis familiaris: Chronology of Tooth Germ Formation and Calcification of Deciduous Teeth

Observations on a sizeable collection of purebred canine fetuses of known age has afforded the opportunity to report baseline data on the timing of tooth germ development in the dog. The chronology of development of the deciduous dentition has been studied in a collection of 172 embryos and fetuses from purebred Beagles of known gestation. Microscopic examination of serial sections, enlarged reconstructions from serial sections and alizarin-stained clearings were used to visualize stages of development. These observations establish that the dental lamina is initiated at 25 days gestation and that calcification begins at 42 days in the deciduous teeth.     

Gross Anatomy of the Canine Portal Vein

The gross anatomy of the portal vein of 21 dogs was studied by venous portography, corrosion casting, and gross dissection. The portal vein in all specimens originated by confluence of the cranial and caudal mesenteric veins. Its large tributaries were the splenic and gastroduodenal veins, which entered the portal vein between its origin and the hepatic porta. At the hepatic porta, the portal vein divided into a short right branch and a larger left branch. The right branch ramified in the caudate process of the caudate lobe and in the right lateral lobe of the liver. The left branch was essentially the continuation of the portal vein from which successive branches passed to each of the remaining lobes of the liver and the papillary process of the caudate lobe.     

Functional Anatomy and Biomechanics of the Canine Hip Joint

Introduction: In many breeds osteoarthrosis of the hip joint is the most typical orthopaedic disease. Numerous studies concerning etiology, pathogenesis and therapy of this disease still consider an exact congruity to be the basis of a physiological joint function. No data, however, are available as far as the distribution of load in the articular surfaces is concerned. Aims: It was the aim of this investigation to describe the biomechanical features of the canine hip joint as exactly as possible with respect to long‐term and momentary loading. Material and Methods: Hip joints from 43 dogs (bodyweight >20 kg) with an average age of 6 years were investigated. The subchondral bone density was determined with the method of CT‐osteoabsorptiometry. With help of cartilaginous and osseus split lines the preferential orientation of the collagen fibres could be determined. In an in vitro experimental setup the contact areas and the contact pressure distribution within the joint have been measured. Results: In the acetabulum, maxima of subchondral bone density were distributed tricentrically: cranially, dorsally and caudally. In the femoral head, only the area close to the attachment of the ligament was highly mineralized. Cartilagineous and osseous split lines within the acetabulum gave evidence of a long‐term tensile stress. In contrast to these findings, there was no clear preferential orientation in the caput ossis femoris. With load increasing initially isolated contact areas extended and became confluent at a loading force of 75% body weight. Values of maximal joint pressure (maximal joint reaction force applied: 400% bodyweight) reached 8–10 MPa. Discussion: The findings clearly show that the articular surfaces of the hip joint are loaded inhomogeneously. For the first time, it was possible to demonstrate that the healthy canine hip joint is physiologically incongruent. Furthermore, areas of cartilage degeneration within the joint surface coincide with regions that are loaded to a higher extent a priori. From the biomechanical point of view it is recommended that all kinds of acetabular fractures – even those affecting the caudal third of the acetabulum – should be surgically repaired in an adequate way.     

Anatomy of the Canine Skull in Low-grade Otocephaly

An inherited low-grade otocephaly in a strain of Beagles was studied. All cases were “mild” with partial agnathia a constant feature in the adult animal. One case of high-grade otocephaly with aprosopus was recorded in an outcrossed animal. Neonatal mortalities in the low-grade type were associated with gross patency of the parietal fontanelle and hydrocephaly. Enlarged lateral ventricles were found in adult dogs, associated with incomplete union of the cranial sutures and occasional membranous-like paietal bone replacement over the patent fontanelle. Partial agnathia was not obvious in the neonate, but became apparent during postnatal skeletal development. The major anatomical differences in the skulls of these dogs were compared with normal Beagles. Malocclusion of the lower mandible and teeth against the upper jaw during development may have resulted in changes in length and width of the upper jaw and certain cranial structures. It was thought that the maloccluding lower jaw acted as a wedge against the upper jaw during mastication and these abnormal pressures, transmitted in an upward, forward, and outward direction, caused lengthening and widening of the palatine and temporal bones, and lengthening of the premaxilla and nasal bones. The nasopharyngeal meatus and palatine fissures were narrower and elongated. The pterygoid processes were pulled into a more horizontal position. It was suggested that a primary inherited abnormality may cause secondary changes in contiguous structures during development, and differentiation between primary (genetic) and secondary (acquired) anatomical abnormalities should be considered.     

Microscopic Anatomy and Enzyme Histochemistry of the Canine Anal Canal

The microscopic anatomy of the anal canal was studied using routine histological methods and the light microscope in male and female dogs ranging from six months to 10 years of age. Precise anatomical boundaries were established for the zona columnaris , the zona intermedia , and the beginning of the zona cutanea. In an effort to clarify conflicting terminology concerning the anal canal, the term "anal sinus" ( sinus anales ) is applied to the shallow troughs located between the longitudinal mucosal ridges or columns (columnae anales) characteristic of the canine and human zona columnaris ; and the term "anal crypt" is used to represent and distinguish the terminal blind pockets of anal sinuses which extend into the lamina propria of the zona intermedia .
Anal glands were identified routinely in the z. columnaris and z. intermedia of the anal canal; dilated excretory ducts of the anal glands were frequently encountered, often filled with inflammatory cells. PAS-positive but Sudan Black-negative secretion was demonstrated in these ducts as well as within the secretory acini. Sebaceous, circumanal and apocrine sweat glands were restricted to the z. cutanea . Moderate to high alkaline phosphatase activity in the basement membrane of circumanal glands may suggest the presence of myoepithelial cells.     

The Intercondylar Fossa of the Normal Canine Stifle: An Anatomic and Radiographic Study

The intercondylar fossa (ICF) in dogs consists of a cranial outlet, intercondylar shelf, caudal arch, caudal outlet, a medial wall, and a lateral wall. The normal cranial outlet is bell-shape and, in mixed-breed dogs (mean body weight 19.2 kg, N = 21), measured 5.8 mm cranially, 8.1 mm centrally, and 10.3 mm caudally. The ICF is oriented 12° from the dorsal plane of the femoral diaphysis and obliqued 7°, proximolateral to distomedial, in the sagittal plane. To adjust for dog size, a fossa width index (FWI) was calculated by dividing the cranial outlet width by the distance between epicondyles. The normal FWI as determined in this study was 0.18 cranially, 0.25 centrally, and 0.32 caudally. The fossa height index was 0.31. Contact between the ICF and the cranial cruciate ligament began at about 115° of extension. The contact area moved cranially in the intercondylar fossa as the stifle was extended. Evaluation of the ICF can be performed radiographically but positioning is critical.