SUMMARY The venous system has been examined by dissection and by making Marco resin casts of the vascular system of young and adult specimens of Phoca vitulina, Halichoerus grypus, Hydrurga leptonyx, Mirounga leonina and Phocaena phocaena. Embryos and foetuses of the above species and of Leptonychotes weddelli, Lobodon carcinophagus, Zalophus californianus, Delphinus delphis, Globiocephala melaena, Balaenoptera physalus and Megaptera novaeangliae have been dissected, injected with coloured gelatin or serially sectioned. A duplicated abdominal posterior vena cava, thin‐walled and of large size, was found in all species examined. A well‐defined sphincter supplied by the right phrenic nerve was found surrounding the posterior vena cava anterior to the diaphragm in all species of Pinnipedia; the sphincter generally consisted of circular bundles of striated muscle, separated from the diaphragm by a fibrous ring. In the Zalophus foetus there was a thin caval sphincter composed of two slips of diaphragmatic muscle. A sphincter‐like “sling” of diaphragmatic muscle was found in Phocaena. A large hepatic sinus was present in all the Pinnipedia examined except Zalophus, but was absent in the Cetacea. A marked stellate plexus of veins on the surfaces of the kidney was present in all species of Pinnipedia. No renal vein emerges from the hilum and the stellate plexus drains by several large vessels into the corresponding limb of the posterior vena cava. The stellate plexus has numerous communications, particularly with an extradural intravertebral vein. A superficial plexus is present, though less marked, in Cetacea, and the main drainage is by one or more renal veins emerging from the mesial slit. The extradural intravertebral venous system is well‐developed in all specimens of Pinnipedia and is present in all adult and foetal Cetacea examined. In Phoca it is in the form of a large vein lying dorsal to the cord, which communicates posteriorly with the stellate renal plexus and the pelvic plexuses, and anteriorly with the intracranial venous sinuses. In Phocaena there is a large vein placed ventral to the cord, but its main communication is with the anterior vena cava. In the Balaenoptera foetus there are two small veins lying ventral to the cord, which communicate with the anterior vena cava via the dorsal thoracic veins. In the latter two species the vertebral canal anterior to the thorax is filled with retial tissue surrounding the cord. In all specimens examined there is only a poorly developed jugular venous system. The intracranial venous drainage would appear to be almost entirely via veins, sinuses or retial tissue in the vertebral canal. The Pinnipedia have a well‐developed azygos system; the Cetacea either a poorly developed one or none at all. All specimens of Pinnipedia, except Zalophus, and those Cetacea examined show a venous plexus or a single vein encircling the pericardium and projecting into the pleural cavity and draining into the thoracic posterior vena cava. Certain experiments carried out on anaesthetiz...
Fat is appreciated as a structural component of synovial joints. It may serve a shock-absorbing function for the incongruent surfaces, vessels and ligaments, but has not been investigated in the posterior sacroiliac joint (PSIJ). Sixty-six cadaveric hemipelves were serially-sectioned and photographed. The amount of visible fat in the PSIJ was quantified using a modified version of Cavalieri’s method. Total volume, fat volume and fat percentage of the PSIJ were calculated in predefined sub-regions. Fat is consistently present in the PSIJ (1.9 ± 1.3 cm3). Fat volume correlates with the PSIJ total volume (p < 0.0001; r = 0.73) and age (p = 0.024; r = 0.24), and is smaller in males (1.4 ± 0.8 cm3) than females (2.4 ± 1.5 cm3). Fat volumes in the middle and inferior sub-regions of the PSIJ show side- (p < 0.0001) and sex-differences (p = 0.013 females, middle sub-region). Age and PSIJ total volume correlate between sexes in various sub-regions (p = 0.05 females superior sub-region; males inferior sub-region). Fat percentage differs between sexes and sub-regions (p = 0.018 females, superior sub-region) but is independent of age and sides. The presence of fat within the PSIJ is a normal finding and shows sex-dependant and age-related differences. It is unclear whether fat is linked to age-related degeneration or has a shock-absorbing role in stress- and load-dissipation in the PSIJ.
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