We observed the cervical vertebrae of a Pacific White-sided Dolphin, and examined gross anatomically the brachial plexus of a specimen stranded at Toyama bay in 2003. The atlas and the axis were fused into one unit. The rest of the cervical vertebrae were free. The brachial plexuses on both sides were formed by the union of the ventral rami of the lower six cervical nerves and the first thoracic nerve. These roots fused with each other to form three trunks on the left side and four trunks on the right side. On both sides, these trunks fused into one band-shaped fascicle. At the axilla, the fascicle radially gave off many nerve branches.
The phrenic nerve and the suprascapular nerve arose from the cranial margin of the plexus. The pectoral nerves arose from the ventral surface of the brachial plexus. In contrast, the subscapular, the axillar, the radial, and the dorsal scapular nerves arose in turn from the dorsal surface of the brachial plexus. The median and ulnar nerves reached the forearm as a common trunk and gave off many cutaneous branches for the skin of the palmar surface of the flipper, and terminated as the palmar digital nerves. The costo-coracoid muscle was innervated by branches from the pectoral nerve and the phrenic nerve and, on occasion, a branch divided directly from the brachial plexus.
The present study and a survey of the literature suggest that the more compressed in length the cervical vertebrae, the greater the increase in number of the ventral rami of the spinal nerves which form the brachial plexus.
The tongues of nine finless porpoise were examined by macroscopy and scanning electron microscopy. The tongues were rectangle-shaped with a blunt apex and were about 4.5-8.5 cm in length and 3.8-5.1 cm in width. The surface of the tongue appeared relatively smooth with no lingual papillae, but there were marginal papillae on the antero-lateral part of the tongue in the young. With growth in length, the following change was observed; ①degeneration of the marginal papillae. ②the connective tissue cores of the marginal papillae changed from dendriform to rod-shaped. ③decrease in the dimension of the facies lingual apex inferioris. ④thickening of the horseshoe-shaped fold under the margin of the tongue. The morphological changes in the tongue of the finless porpoise were thought to be related to sucking and suction-feeding.
Pacific white-sided dolphin (PWS) Lagenorhynchus obliquidens is the most common cetacean species found in the Tsugaru Strait, Japan. This paper estimates the population of PWS migrated in the strait. The sighting records were collected from the sighting survey in the strait between 2004 and 2010. The PWS population was estimated by using the line transect method for two periods; March to July and May, which is responds to the migration season and mostly observed season. From the limitation of the number of data, the all data from 2004 to 2010 were pooled and estimated the average population. In for March to June, the average estimated population was 4,482 (CV=0.192) and effective strip width was 111.75m. In May the total estimated population of PWS was 9,592 (CV=0.251) and effective strip width was 109.45m. Comparing to the result of the previously reported studies, it was suggested that part of PWS at the coast of both Sea of Japan and Pacific migrate to Tsugaru Strait and most of them use different routes.
Following a previous paper (Honma, et al.,2010), stranding, entangling, and sighting records of marine mammals along the beach and offshore regions of Niigata Prefecture, the Sea of Japan , were compiled from January 2009 to May 2010, in order to made comparison among the instances of previous years investigated 1994－2008. As a result,
5 stranding, 2 Minke whale entangling, and 154 sighting instances, consisting of 141 on the Niigata ~ Ryotsu route, 5 on the Naoetsu~Ogi route, and 8 in the offshore coast of Kashiwazaki by whale watching boats, were noted. The striking numbers (141) indicated the largest than for of previous years, and were reported elsewhere (Honma and Iwashita 2010 ). A small number of stranding records seems to be dependent on a few rough storms occurred in winter. Many individuals of Dall’s porpoises were observed on the car ferry operating on the Naoetsu~Ogi route. A stranding beaked whale was inspected macroscopically from the pathological point of view.