Characterising injuries and pathologies of common dolphin Delphinus delphis mortalities in the South Australian Sardine Fishery.

Mortality of dolphins in fishing operations is often under-estimated, as shown by studies of beach-washed carcasses. Linking evidence obtained during necropsies with fishing method is fundamental to understanding the extent of mortality and the manner in which animals die. The South Australian Sardine Fishery (SASF) has operated a purse-seine industry since 1991. This study characterised injuries, pathological changes and life history of 49 dead dolphins collected from SASF during 2006-2019. Histology examination was conducted on 25 animals. Neonates, calves and juveniles accounted for 63% of the sample. Of mature females (n = 14), 11 were pregnant or lactating, with cryptic mortality estimated to be 20% of dolphins studied. Body condition was robust in 48 dolphins. Net marks were seen on 82%, mostly on the head, trunk and peduncle. Broken/missing teeth were noted in 63%. All dolphins had subdermal haemorrhage (moderate to severe in 96%), particularly around the head. Deep haemorrhage was common, including around occipital and flipper condyles, and organs. Copious fluid was present in the thoracic (pleural) and abdominal (ascites) cavities of half of the dolphins. Within the lungs, watery fluid and froth were observed in 100 and 39%, respectively. Recent bone fractures were documented in 43% of dolphins, mostly associated with haemorrhage. Severe blunt trauma appeared to be the primary cause of death, and 10 dolphins also had other significant pathologies. Visceral organ congestion and mild cardiomyopathy were observed. Stomachs contained prey remains in 75% of cases. The results of this study may help identify unreported purse-seine mortalities washed up in South Australia and elsewhere.

Development of mandibular cartilages in the rat.

BACKGROUND: The mammalian mandible develops around Meckel's cartilage and other secondary cartilages, including the dentary. There have already been many studies of the development of the rat mandible that have employed histological serial sections. However, no previous investigators have captured the three-dimensional features of the developmental process. METHODS: In this study, the technique of double staining with alizarin red S and alcian blue was employed directly on whole body specimens to investigate the three-dimensional development of the rat mandible. RESULTS AND CONCLUSIONS: We found that the molar socket obstructs the developing mandible, causing it to emerge medial to Meckel's cartilage. Our results also indicate that the secondary mandibular cartilages may contribute to supplementary growth in response to local factors.

Digastric muscle of the kangaroo: a comparative anatomical study.

Although the human digastric muscle is classified as a suprahyoid muscle, none of the digastric muscles in other mammals are classed as suprahyoid in textbooks of veterinary anatomy. The aim of this study was to describe the anatomical relationship of the digastric muscle in a marsupial, the kangaroo, and to consider factors thought to be important in leading to the different position of the muscle in quadrupeds compared with humans. Eight heads of the common wallaroo (Macropus robustus) were used in this study. They were fixed by injection of 10% formalin solution into the carotid arteries and dissected under a stereomicroscope. The digastric muscle in the common wallaroo arose from the paroccipital process of the temporal bone and inserted into the mandible but had no intermediate tendon or any connection with the hyoid bone. It was supplied by both the mandibular and facial nerves. The hyoglossus muscle attached to the inferior surface of the hyoid bone and its ventral border overlapped the mylohyoid muscle. The hypoglossal nerve passed between these two muscles. Therefore, in contrast to humans, the digastric, hyoglossus, and mylohyoid muscles in the kangaroo were all located inferior to the hyoid bone. Differences in head posture and the position of the larynx between kangaroos and humans may account for the observed difference in the digastric muscle's position relative to the hyoid bone between these species.

The morphology and innervation of the lateral pterygoid muscle of the dog.

The number of heads possessed by the lateral pterygoid muscle was investigated in the dog. Only a single head was observed which it is suggested may correspond to the lower head in other mammals. It inserted both onto the condyle and into the articular disc. The nerve which innervated this muscle arose directly from the mandibular nerve, separate from the medial pterygoid nerve. Because of this, it should be termed the lateral pterygoid nerve and not the pterygoid nerve.